Light - CBSE

CLASS
VI
CBSE-i
SCIENCE
PHYSICS
Light
UNIT-3
Shiksha Kendra, 2, Community Centre, Preet Vihar, Delhi-110 092 India
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translate copyright material used in this publication.
The
acknowledgements have been included wherever appropriate and
sources from where the material has been taken duly mentioned. In
case anything has been missed out, the Board will be pleased to rectify
the error at the earliest possible opportunity.
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may be reproduced, printed or transmitted in any form without the
prior permission of the CBSE-i. This material is meant for the use of
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Preface
The Curriculum initiated by Central Board of Secondary Education -International (CBSE-i) is a progressive step in making
the educational content and methodology more sensitive and responsive to the global needs. It signifies the emergence of a
fresh thought process in imparting a curriculum which would restore the independence of the learner to pursue the
learning process in harmony with the existing personal, social and cultural ethos.
The Central Board of Secondary Education has been providing support to the academic needs of the learners worldwide. It
has about 11500 schools affiliated to it and over 158 schools situated in more than 23 countries. The Board has always been
conscious of the varying needs of the learners in countries abroad and has been working towards contextualizing certain
elements of the learning process to the physical, geographical, social and cultural environment in which they are engaged.
The International Curriculum being designed by CBSE-i, has been visualized and developed with these requirements in
view.
The nucleus of the entire process of constructing the curricular structure is the learner. The objective of the curriculum is to
nurture the independence of the learner, given the fact that every learner is unique. The learner has to understand,
appreciate, protect and build on values, beliefs and traditional wisdom, make the necessary modifications, improvisations
and additions wherever and whenever necessary.
The recent scientific and technological advances have thrown open the gateways of knowledge at an astonishing pace. The
speed and methods of assimilating knowledge have put forth many challenges to the educators, forcing them to rethink
their approaches for knowledge processing by their learners. In this context, it has become imperative for them to
incorporate those skills which will enable the young learners to become 'life long learners'. The ability to stay current, to
upgrade skills with emerging technologies, to understand the nuances involved in change management and the relevant
life skills have to be a part of the learning domains of the global learners. The CBSE-i curriculum has taken cognizance of
these requirements.
The CBSE-i aims to carry forward the basic strength of the Indian system of education while promoting critical and
creative thinking skills, effective communication skills, interpersonal and collaborative skills along with information and
media skills. There is an inbuilt flexibility in the curriculum, as it provides a foundation and an extension curriculum, in all
subject areas to cater to the different pace of learners.
The CBSE has introduced the CBSE-i curriculum in schools affiliated to CBSE at the international level in 2010 and is now
introducing it to other affiliated schools who meet the requirements for introducing this curriculum. The focus of CBSE-i is
to ensure that the learner is stress-free and committed to active learning. The learner would be evaluated on a continuous
and comprehensive basis consequent to the mutual interactions between the teacher and the learner. There are some nonevaluative components in the curriculum which would be commented upon by the teachers and the school. The objective
of this part or the core of the curriculum is to scaffold the learning experiences and to relate tacit knowledge with formal
knowledge. This would involve trans-disciplinary linkages that would form the core of the learning process. Perspectives,
SEWA (Social Empowerment through Work and Action), Life Skills and Research would be the constituents of this 'Core'.
The Core skills are the most significant aspects of a learner's holistic growth and learning curve.
The International Curriculum has been designed keeping in view the foundations of the National Curricular Framework
(NCF 2005) NCERT and the experience gathered by the Board over the last seven decades in imparting effective learning to
millions of learners, many of whom are now global citizens.
The Board does not interpret this development as an alternative to other curricula existing at the international level, but as
an exercise in providing the much needed Indian leadership for global education at the school level. The International
Curriculum would evolve on its own, building on learning experiences inside the classroom over a period of time. The
Board while addressing the issues of empowerment with the help of the schools' administering this system strongly
recommends that practicing teachers become skillful learners on their own and also transfer their learning experiences to
their peers through the interactive platforms provided by the Board.
I profusely thank Shri G. Balasubramanian, former Director (Academics), CBSE, Ms. Abha Adams and her team and Dr.
Sadhana Parashar, Head (Innovations and Research) CBSE along with other Education Officers involved in the
development and implementation of this material.
The CBSE-i website has already started enabling all stakeholders to participate in this initiative through the discussion
forums provided on the portal. Any further suggestions are welcome.
Vineet Joshi
Chairman
Acknowledgements
Advisory
Shri Vineet Joshi, Chairman, CBSE
Shri Shashi Bhushan, Director(Academic), CBSE
Ideators
Ms. Aditi Misra
Ms. Amita Mishra
Ms. Anita Sharma
Ms. Anita Makkar
Dr. Anju Srivastava
Dr. Indu Khetarpal
Ms. Vandana Kumar
Ms. Anju Chauhan
Ms. Deepti Verma
Ms. Ritu Batra
Conceptual Framework
Shri G. Balasubramanian, Former Director (Acad), CBSE
Ms. Abha Adams, Consultant, Step-by-Step School, Noida
Dr. Sadhana Parashar, Head (I & R),CBSE
Ms. Anuradha Sen
Ms. Jaishree Srivastava
Ms. Archana Sagar
Dr. Kamla Menon
Ms. Geeta Varshney
Dr. Meena Dhami
Ms. Guneet Ohri
Ms. Neelima Sharma
Dr. Indu Khetrapal
Dr. N. K. Sehgal
Material Production Group: Classes I-V
Ms. Rupa Chakravarty
Ms. Anita Makkar
Ms. Anuradha Mathur
Ms. Kalpana Mattoo
Ms. Savinder Kaur Rooprai
Ms. Monika Thakur
Ms. Seema Choudhary
Mr. Bijo Thomas
Ms. Kalyani Voleti
Dr. Rajesh Hassija
Ms. Rupa Chakravarty
Ms. Sarita Manuja
Ms. Seema Rawat
Dr. Uma Chaudhry
Ms. Nandita Mathur
Ms. Seema Chowdhary
Ms. Ruba Chakarvarty
Ms. Mahua Bhattacharya
Material Production Groups: Classes VI-VIII
English :
Ms. Rachna Pandit
Ms. Neha Sharma
Ms. Sonia Jain
Ms. Dipinder Kaur
Ms. Sarita Ahuja
Science :
Dr. Meena Dhami
Mr. Saroj Kumar
Ms. Rashmi Ramsinghaney
Ms. Seema kapoor
Ms. Priyanka Sen
Dr. Kavita Khanna
Ms. Keya Gupta
Mathematics :
Ms. Seema Rawat
Ms. N. Vidya
Ms. Mamta Goyal
Ms. Chhavi Raheja
Political Science:
Ms. Kanu Chopra
Ms. Shilpi Anand
English :
Ms. Sarita Manuja
Ms. Renu Anand
Ms. Gayatri Khanna
Ms. P. Rajeshwary
Ms. Neha Sharma
Ms. Sarabjit Kaur
Ms. Ruchika Sachdev
Geography:
Ms. Deepa Kapoor
Ms. Bharti Dave
Ms. Bhagirathi
Ms. Archana Sagar
Ms. Manjari Rattan
Mathematics :
Dr. K.P. Chinda
Mr. J.C. Nijhawan
Ms. Rashmi Kathuria
Ms. Reemu Verma
Science :
Ms. Charu Maini
Ms. S. Anjum
Ms. Meenambika Menon
Ms. Novita Chopra
Ms. Neeta Rastogi
Ms. Pooja Sareen
Political Science:
Ms. Sharmila Bakshi
Ms. Srelekha Mukherjee
Economics:
Ms. Mridula Pant
Mr. Pankaj Bhanwani
Ms. Ambica Gulati
Geography:
Ms. Suparna Sharma
Ms. Leela Grewal
History :
Ms. Leeza Dutta
Ms. Kalpana Pant
Teacher Notes :
Ms. Suman Nath
Material Production Groups: Classes IX-X
Dr. Sadhana Parashar,
Head (I and R)
Shri R. P. Sharma, Consultant
Ms. Seema Lakra, S O
History :
Ms. Jayshree Srivastava
Ms. M. Bose
Ms. A. Venkatachalam
Ms. Smita Bhattacharya
Coordinators:
Ms. Sugandh Sharma,
Dr. Srijata Das,
Dr. Rashmi Sethi,
E O (Com)
E O (Maths)
E O (Science)
Ms. Ritu Narang, RO (Innovation) Ms. Sindhu Saxena, R O (Tech) Shri Al Hilal Ahmed, AEO
Ms. Preeti Hans, Proof Reader
Shri Vikram Yadav, Proof Reader
CONTENT
PREFACE
ACKNOWLEDGMENT
PHYSICS : LIGHT - SYLLABUS
1
SCOPE DOCUMENT
3
- CROSS CURRICULAR LINKS
3
MATRIX
4
TEACHER NOTES (TN)
5
TEACHER STUDENT SUPPORT MATERIAL (TSSM)
13
LIGHT: INTRODUCTION
13
ACTIVITY 1
13
LIGHT: ITS PROPERTIES
15
ACTIVITY 2A, 2B, 2C
17,18
CLASSIFICATION OF OBJECTS- LUMINOUS AND NON LUMINOUS
20
ACTIVITY 3
20
FORMATIVE ASSESSMENT 1
21
WORKSHEET 1 & 2
23
CLASSIFICATION OF MATERIAL- TRANSPARENT, TRANSLUCENT, OPAQUE 25
ACTIVITY 4
25
FORMATIVE ASSESSMENT 2
28
LIGHT AND SHADOW FORMATION
29
ACTIVITY 5
31
ACTIVITY 6 & 7
34,35
ACTIVITY 8 & 9
36,37
SHADOW FORMATION IN NATURE: ECLIPSE
38
LIGHT AND ITS APPLICATION: MIRROR AND REFLECTION, PERISCOPE, PINHOLE CAMERA
WORKSHEET 3
46
SUMMATIVE ASSESSMENT
48
RUBRIC FOR ASSESSMENT
55
SUGGESTED VIDEO CLIP/WEB RESOURCES
56
PHYSICS
Unit IV : Light
CONTENT
S
1. Light: An introduction.
Y
2. Properties of light.
L
3. Rectilinear propagation of light.
L
4. Luminous and non-luminous objects.
A
5. Transparent, Translucent and Opaque Materials.
B
6. Shadows and their formations.
U
7. Mirrors and Reflection.
S
8. Light and its Applications
Science
1
LIGHT
This unit is meant to develop the knowledge of some of the simple basic properties of light.
It will also help the students to understand and explore about the various phenomena of
light in day-to-day life. It is intended to empower the learners to feel confident that proper
knowledge of concepts provides us with the ability to use information and technology
that suits the needs of the people.
2
Science
SCOPE DOCUMENT
INTENDED LEARNING OUTCOMES:
At the end of this unit, students would be able to:
Identify different ideas and words related to light.
F
Understand and identify the types of light rays.
F
Gain evidence that light propagates in a straight path.
F
Differentiate between luminous and non-luminous objects.
F
Identify some common luminous and non-luminous objects.
F
Describe the terms: transparent, translucent and opaque.
F
Differentiate between transparent, translucent and opaque objects.
F
Carefully observe the formation of shadows in different time.
F
Mention the cause of the formation of shadows.
F
Use conceptual clarity to identify types of eclipses.
F
Understand the meaning of reflection of light.
F
Differentiate between regular and irregular reflection.
F
Explore the phenomenon of reflection in a periscope.
F
Cross curricular links
Chemistry- Apply concepts of types of materials
F
(Transparent, translucent and opaque)
Mathematics - Apply concepts of drawing, reading and interpreting angles.
F
English/Languages -Articulation and sharing information, writing investigation
F
plans, vocabulary.
Information Technology - Making PowerPoint presentation using animation
F
tools, research work.
Biology- Formation of image on the retina.
F
Astronomy - Study of eclipses.
F
Art- Use tools, materials and techniques properly, selecting those that are
F
appropriate for the work.
Science
3
MATRIX
Content/concepts
Intended Learning
Skills
Introduction: Light; To understand that light helps us to Observation.
its Importance ,
see and differentiate between Appreciation of scientific
properties of Light various colours of the objects.
contributions.
Rectilinear
propagation of light. Light travels in a straight line.
How light travels?
Classification of
objects as Luminous Differentiate between luminous
and Non Luminous, and non-luminous objects.
different examples.
Classification of
materials in terms of
their behaviour
towards light.
Transparent,
translucent and
opaque.
Light and Shadow;
its formation,
measurement and
its parts. Shadows
in natural
phenomenon e.g.
eclipse.
Use of properties of
Light, Mirrors and
reflection.
4
To familiarise the students with
different types of materials:
transparent, translucent and
opaque.
Appreciate the use of classification
in day to day life.
To see how and why shadows are
formed.
Measurement of the size of
shadows.
To identify and relate the image
formed by a mirror and to list its
characteristics.
Learning by doing, careful
observation.
Relating the understanding
with day to day life.
Observation, learning by
doing.
Understanding and
making connections.
Understanding, observation
and reasoning.
Hypothesis formation
Observation, learning by
doing, accuracy in
measurement. Manage,
record and communicate
information.
Careful observation of the
natural phenomenon.
Observation and
understanding, connecting
the properties of light in
day to day life.
Science
TEACHER NOTES (TN)
The unit can begin by creating a great sense of appreciation among the students that the
beautiful world we see around us is due to the availability of light. Our eyes enable us to see
the objects only when light falls on them. The teacher could give to the students an activity
(Activity 1) by which they will be able to appreciate the importance of light in making our
world visible to our eyes. This activity will help the learners enhance their observational
skill and relate it to the importance of light.
The teacher could make a collection of concepts related to the phenomenon of light for the
main teaching points, keeping in mind the Intended Learning Outcomes.
Discussion on terms like brightness, shades, colours, shadows etc. would provide a great
resource from the students. This would help you to assess the learning attainment and yet to- be attained concepts regarding light and its behavior. It depends how smartly you
would be able to note the misconceptions or intuitive understandings of students as a
whole. It would greatly help to redesign your next interactions based on this feedback to
promote further learning about the unit This could promote inquiry based interest in
students.
It will be interesting to take up a simple but rarely entertained observation about colour.
Ask the students the colour of light. After eliciting various answers the teacher could show
them the scattering of light through a prism thus further arousing their curiosity by seeing
different colours in white light. You could ask the students to name these colours and list
them on the board in a sequence so as to make the word VIBGYOR. The learners will hence
gain the knowledge about what each letter of VIBGYOR stands for. Also they would see the
same organization of colours as VIBGYOR in natural spread of colours. Try to get these
answers from the students so that they remain enthusiastic to participate in developing the
concept. In order to enhance the thinking skills of the students you could ask them to give
examples of the phenomena that show the pattern of light consists of seven colours. At this
point the idea of rainbow formation could be shared with them.
You may inform them about human enterprise to learn from nature and create its
representation in artificial situations. The discussion on the prism can be re looked at this
point. Let the learners hold the prism and try to see different objects through it. Spend some
time on this activity and record the learners' responses.
Science
5
The use of prism serves few purposes, such as:
l
Observation of colour and scattering of light,
l
the order of the colour in VIBGYOR pattern
l
artificial rainbow which does not bow but is straight.
l
It can
be inductively concluded that Light travels in a straight line unlike a rainbow
which moves through rain drops.
For an extended learning the scattering of light in colours, abbreviated as VIBGYOR,
created by moisture/water droplets present in the atmosphere could be taken up in the
class. The learners could then be given an opportunity to apply their knowledge to
conclude the reason for the appearance of rainbow after a spell of rain. For further
strengthening the extended learning they could be explained why they are not able to see
the rainbow after every spell of rain.
An activity involving paper folding to make a hand fan could be given to the students to
help them prove experimentally that white light emitted by the sun consists of seven
colours. This fan could have seven wings, each painted with a single colour in the order of
VIBGYOR. The students could be asked to rotate the fan and be surprised to see when
wings are rotated at a fast speed, no single colour becomes visible but what they can see is
only white colour. This exercise informs us about the ability of the eye to see colours at
different speeds. As an expression of art you could ask students to make a colour chart
using water colours, beginning with primary colours red, blue and yellow.
This concept could lead to a discussion on why leaves look green, flowers show red, yellow
or orange colour and some objects look black while others look white. The connection of
light, colour and life is crucial for wholistic learning about our surrounding. These are
the moments that carry the scope to ignite interest in inquiry into how things operate, what
principles guide different phenomena that we come across in daily life. The attitude to take
things for granted, limits learning. This can be minimized by encouraging and
demonstrating inquiry approach in class interactions.
You could connect this to the introduction of the topic stating that we are able to see objects
when light falling on the objects reflects and reaches our eyes. The concept of reflection of
light could be initiated and the learners could be stepwise enabled to conclude when white
light falls on a leaf it looks green as it reflects green colour and absorbs all other colours. The
learners would be able to derive corollary to that, logically and will be able to explain why
6
Science
they see objects of different colours. An object looks black because it absorbs all colours of
light and does not reflect any light whereas it looks white because it reflects all colours and
does not absorb any light.
At this point you could inform students about the properties of light in some detail. The
learners could be given an activity showing how light enters a dark room through a small
hole. To enhance their observational skills they could be asked what they observe to share
orally or in written form.
By this activity the terms 'beam of light' or 'ray of light' could be introduced. Hence,
vocabulary development could go hand in hand.
You could make the students perform activity 2a and activity 2b in TSSM to facilitate in
understanding the property of light .It travels in a straight line. The demonstration of
activity 2c will further clear the concept of Rectilinear Propagation of light. This activity
would also trigger the students in going beyond what the teacher is trying to get at and it
could make them explore the answer to their own curiosity about the medium in which
light would travel. Does light need a medium to travel?
A brain storming session could be organized by the teacher whereby the learners could
give their own ideas on the change in the speed of light vis-a-vis medium through which it
travel. The learners could be asked if the speed of light the same in air, water or in vacuum.
This could also give an opportunity to them to do some research on the internet to explore
the behavior of light in different media.
You could explore the creative, imaginative and intelligent guessing (inferring) ability of
the learners by inquiring: if the speed of light is the same, slower or faster than the speed of
sound. Since students are not a blank slate but curious observers, trust their potential and
wait for their observation on the bursting of crackers during festival. You could take their
attention to the thunder and lightning in the sky. With little probing you could extract the
answer that they first see the fire of a cracker and later they hear the sound hence proving
the fact that light travels faster than the speed of sound.
You could ask the students to give examples of the property of light stating that light
travels in a straight line. By eliciting examples from the learners you could encourage them
to apply their knowledge and understanding of the concepts in their day-to-day life
situations. Careful observation of examples such as formation of shadows, beam of a
search light, light of car's headlight and so on would pave way for a scientific outlook in
Science
7
life.
You could show the learners a glowing electric bulb, a wooden chair and ask them to
compare these two with that of Sun. A discussion session could help you to get at a
conclusion from the learners that an electric bulb glows and gives light, wooden chair does
not glow on its own but can be seen only when light falls on it. Luciferin is a pigment found
in animals which is responsible for the shine and light emitted by them.
You could then enhance learners' vocabulary by using the term Luminous for bodies that
are the source of light and Non-Luminous for bodies that can be seen only when light falls
on them. The students will be able to differentiate between luminous and non-luminous
objects.
Explain to students how:
F
Formation of day and night.
F
Formation of shadows at different positions during the day
Kindly note that luminosity is the feature of light associated with a cold object e.g. radium,
whereas, light associated with a hot object is called incandescence. So the examples quoted
above like 'glowing bulb' & 'sun' are incandescent objects. You may pose challenging
situations to test their understanding e.g. a photograph of sun & natural sun, a burning
candle and just a candle, fire fly etc. It will be a good idea to ask the learners to differentiate
between Sun as the source of light and an electric bulb as the source of light.
Through a brain storming session you could elicit examples from the students of natural
luminous resources such as fire-fly, Sun and Stars and man-made (artificial) luminous
sources such as candle, electric bulbs, tube lights. This would enhance their thinking skills.
The skill to carefully observe the things and phenomena in the surroundings in their
dynamic state is itself a great life long learning that gets transcribed into the rational
attitude to life.
Worksheet 1 and 2 will help the students to re-enforce the concepts and also help them to
apply it in their day-to-day knowledge and will strengthen their experiential learning.
Sometimes liquids kept in coloured bottles show a different colour than their actual colour.
It could be demonstrated how different objects such as plain glass tumbler, a coloured
glass tumbler and a steel glass tumbler behave when light falls on them. To enhance the
learners' observational skills they could be asked to view a pencil box kept at the back of the
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Science
tumbler while the light source is placed in front of the tumbler such that the light falls on
the tumbler directly. Learners could be asked to note their observations and share the same
with other class mates. They will be able to reason out the differences among the three
types of objects. The terms Transparent, Translucent and Opaque could also become part
of their vocabulary development.
It would be important to link this point with the unit 1, on Classification of Materials where
properties of material and visibility have been introduced. Doing so, will make better
connections in the conceptual development of the learners. At the same time make learning
less burdensome and more joyful. Your role as a reflective practitioner is important.
Integration can be with same concept treated in different units or under the same
theme/issue.
Learners would be able to differentiate among three types of objects based on how much
light passes through them. They could be given an opportunity to explain the behavior of
diamond. Will they call it a transparent object or a luminous object? Adequate time must be
given to explore the same in order to apply their theoretical knowledge. Students could
make a list of transparent, translucent or opaque objects other than these discussed in the
class to re-enforce their experiential learning.
You could inquire: Is it the light alone or the property of the object or the medium through
which light passes that influence the behavior of the light? It could generate a plethore of
opinions, beliefs, mis concepts, facts, principles from the students.
The concept of types of objects could lead the learners to draw a corollary that shadow is
formed only when the light falling on an object is not able to pass through the object. This
could be taken as the beginning of discussion on what shadows are, how they are formed,
if they are always formed and if they are of the same size at all times. Frame questions prior
to the teaching so as to connect it to the conceptual understanding. Framing of precise and
clear questions is a skill that can be an asset for a teacher to communicate the concepts
effectively.
The teacher could ask the learners to observe the shadow of a tree formed at different times
of the day and note down their observations. This will not only develop an attitude among
the learners about experimental and observational skill but also help them to enhance their
data entry skills.
A discussion among students will facilitate the answer that shadow by the Sun is the
Science
9
largest in the morning and evening time whereas it is the shortest during noon time.
Students could be given a group or an individual project to measure the size of the shadow
of an object (planted or placed) in an open area at different parts of the day. The students
will be able to observe that the length of the shadow of an object in daylight is different at
different times of the day. This would enhance their ability to measure the length of the
shadow accurately (unit 0 on Measurement). Show/inform/discuss or ask students to find
out about Architectural wonder as Jantar Mantar in India, where the calculation of time is
done by measuring the shadow. You could demonstrate an activity to initiate the project
work. In order to enhance their data collection and data recording skills, you could ask the
learners to fill up the columns given in the table. Depending on your previous interactions
you may either provide a table or ask students to make a table. This could help you assess
their ability to organize and present data in a simple and effective way.
As an extended learning they could be asked to make an observation on the direction at
which the shadow is formed and relate it to the direction of the Sun at different time
intervals, vis-s-vis the object. They should be able to mention that shadow is formed
opposite to the direction of the Sun. Take the attention of the students to day and night
matches and formation of shadow.
You may refer Plato's 'Allegory of the Cave' as an extended reading for yourself. The
writing is philosophical and addresses bigger question of ignorance and of knowledge in
life. Such classical works lend a perspective to see the world of ideas. You may build your
own perspective through reading perspectives offered in classical literature. You would
appreciate the fact that many scientists were also philosophers. Both Science and
philosophy attempt to respond to the big questions related to life but only differ in their
approach.
It is important for learners to know if the size of the shadow of an object remains the same.
You could demonstrate the activities to show shadow formation by changing the positions
of the object, source of light and the screen on which the shadow is viewed. The learners
could be asked to observe these activities and thus empowering them to find the factors on
which the size of shadow depends. Learners could then conclude that a) the size of shadow
depends on the distance between the object and the screen as well as b) the distance
between the object and the source of light. Learners could be asked to derive the
relationship among the positions of object, source of light and the screen on which the
shadow falls with respect to the size of the object. An intelligent guess game for hypothesis
building can be done in the class after the concept is taught.
The activity will re-enforce what they learnt earlier that the size of the shadow of an object
on the wall depends on its location with respect to the light source and the wall. The factors
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Science
that affect shadow formation may be noted and listed by the students to understand how
shadows form and can be created by changing these factors.
They could be asked to find the cause of formation of shadows and conclude that the image
is formed only when there is an obstacle between the object and the source of light. Activity
6a will re-enforce the understanding of this concept of the parts of a shadow i.e. Umbra and
Penumbra. Try to elicit the conclusion from the learners that the size of Umbra and
Penumbra depends on the distance between screen and obstacle. i.e. the object. You may
ask and reflect: Will sun have a shadow?
As an interesting activity encourage the learners to explore the use of knowledge of
shadows creatively. Help them create different shapes by the shadows of the hand, fingers,
etc. in a dark room by only allowing a beam of light falling on the hands. This activity will
bring out a form of art, probably a hidden talent in learners.
The students could be given a group project on application of rectilinear propagation of
light. They could come up with the idea of making a pin-hole camera. You could explain
the working of a pin-hole camera.
While recapitulating the students' previous knowledge about the rotation of the earth
around the moon and of the moon around the sun and the earth, students could be
encouraged to imagine as to what will happen if the sun, moon and earth come in a straight
line? What could be the situation when : the earth becomes an obstacle between the sun and
the moon and when moon becomes an obstacle between the sun and the earth? The
phenomena of Lunar and Solar eclipse and reasons to differentiate between Lunar and
solar eclipse could be explained.
Question as why must the earth or the moon do so? Why does not the sun become an
obstacle, may be asked to anchor the concepts in a well connected way. The presentation
would largely decide to create or kill the interest to know about macro phenomenon of
eclipse. Astronomical interests get generated by careful and intelligent presentation of
concepts which may appear to be difficult for class VI, yet the curiosity to know can always
be created. Realize the crucial role you can play in promoting the future scientists through
your teaching and facilitation.
By drawing the diagrams on the board, you could demonstrate the formation of eclipses
using simple equipments and explain regions of umbra and penumbra in it.
Take the opportunity to discuss practices related to the occurrence of eclipse. Be cautious
not to explode every practice as a myth. Take time and collect information to come out with
a hypothesis. The attempt to smash old practices as myths could be reflective of scientism
Science
11
rather than a scientific attitude to arrive at logical explanations. Scientism is having faith in
science which is against the nature of science. Of course! you could help to remove
unfounded practices by adequate scientific information. In fact a multicultural classroom
can be most suitable avenue to demystify the notions about eclipses. This could be quite
Challenging but a meaningful step to learning.
In addition, you could also demonstrate how to view solar eclipse safely as looking at the
sun directly during the solar eclipse could be harmful for the eyes. Why?
The concept of Reflection of Light can be further strengthened by organizing a discussion
session among the students on working of mirrors. The students could be explained the
principle of Reflection of Light. You could show them different types of mirrors for them to
view image of objects through. To enhance their knowledge they could be explained the
concept of using the rear mirrors in vehicles. These are not ordinary mirrors but
converging mirrors. Let them pause to think how can converging mirrors be created. They
may do a project work on it to find out the story of the creation of a converging mirror.
For an extended learning the students could apply their knowledge about reflection
through the mirrors and the principle of rectilinear propagation of light to make a
periscope. They could be given this as a group project. You could explain to them the
working of a periscope. To enhance the drawing skills of the students, they could be asked
to make ray diagrams to show the image formation through a periscope. The class may be
divided into groups and each group could be given the task of listing the applications of
periscope and mirrors.
A fun activity could be organized to have a volunteer group make a kaleidoscope and the
teacher could explain the concept of multiple image formation and also, the terms real
images and virtual images could be introduced.
Through this unit the teacher will be able to involve the participation of students in the
teaching learning process. The observational, experimental, thinking and drawing skills
will be enhanced. The students will get ample opportunity to apply their knowledge in
their day-to-day experiences.
Worksheets and / or questionnaires could be given to the students for formative and
summative assessment. Prepare your worksheets or tasks suiting the readiness to learn of
the among students.
You may organise the concepts in an order that enables articulation one such way is
provided here
Optic, shadow, umbra penumbra, energy form of energy, rectilinear, straight movement,
propagation, space, vaccum, air.
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Science
TEACHER STUDENT SUPPORT MATERIAL (TSSM)
LIGHT
1. INTRODUCTION:
This unit focuses on Light, the basis of Visual World around us. The main focus is going to
be on the properties of light, the behaviour of materials towards light, shadows and the
related study about eclipses.
Discuss general concepts related to LIGHT, SIGHT, COLOUR, SENSE ORGAN and
VIBGYOR . Brain storm with questions like, how does light look like? What role does it
play in our lives? How it moves or travels? How does light behave? Is it always the same? Is
it usually the same? What are the different patterns of light that we can see?
ACTIVITY 1: LIGHT AND VISION
Learning outcome: Student would be able to sense that light helps us to see various objects
around us.
Procedure:
Switch off all the lights and cover the glass window with black papers or close the doors
and draw on the curtains so that the room becomes completely dark. Can we see each
other? Can we see the things around us?
Now make a hole in any one of the black papers on the window or remove one of the
curtains. We will observe a beam of light entering the room. We can see the object/objects
on which the rays of light fall see picture 1 below.
Picture 1
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13
Conclusion:
When light falls on objects, it gets reflected from them. When this reflected light reaches
our eyes, we are able to see the objects. The colour of the objects that we see depends upon
the colour of the light, the object reflects.
As we all know that light consists of seven colours which are represented by VIBGYOR.
The seven colours are V- Violet, I- Indigo, B- Blue, G- Green, Y- Yellow, O- Orange, R- Red
can be seen in the same order. If an object appears to be green, it means that the object
absorbed all the colors of light except green which gets reflective. This colour reaches our
eyes and we see the object as green . See picture 2 below.
Dispersion of Light through a Prism.
Picture 2
Light is a form of energy which our sense of sight can detect. It is a portion of electromagnetic radiation. It does not require any material as medium such as air, water, metal
etc. to travel from one place to another. We are able to see the beautiful and colourful world
around us because of light.
One of the most important discoveries about light is the calculation of the speed at which it
travels in vacuum. Light travels at a speed of 300,000 kilometers per second (3x108 m/s).
While movies like Star Wars and Star Trek often show spaceships blasting across the
Universe moving faster than light, scientists believe that the speed of light is the upper limit
for how fast objects can travel. However, speed of light can be changed. It becomes slow
when it is made to pass through other medium/media such as water or glass. Speed of light
is taken to be the same for air and vacuum in most of the cases.
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Science
You may wonder:
How would have scientist measured the speed of light? What is the use of knowing the
speed of light?
The speed of light is an important value for many reasons; one of the most practical use is
to help us calculate astronomical distances (distances between planets or stars.) and to
determine how long it will take communication signals(a form of light) to travel through
space.
Fig. 1 Electromagnetic spectrum with light (highlighted)
2 PROPERTIES OF LIGHT
Many a times we have observed the light entering through a door or a window in the
room. In the picture below what do you observe? We can note rays of light entering
through the door and falling on the objects in the room. This is actually how light travels.
Picture 3
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15
A ray of light is a quite narrow straight path which is used to show the propagation of light
with or without a medium. Generally, a straight line is used to represent a ray of light. An
arrow is put on it to indicate the direction of propagation of light. In the picture above we
can see many straight lines. What does this mean? We usually see a bundle of rays and not a
single ray, which is called a beam.
Ray of light
Beam of light
A beam of light is the collection of a large number of light rays. A parallel beam is a
collection of parallel rays emitted by a (far-off) luminous object. It may be celestial body as
sun or burning candle.
The arrow indicates the direction of the rays.
Parallel beam of light
The following activities can be taken to explain that light travels in a straight line. We also
call this as the rectilinear propagation of light. The teacher can demonstrate this property
through these activities.
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Science
3 RECTILINEAR PROPAGATION OF LIGHT
ACTIVITY 2A : PATH OF LIGHT
Learning outcome: Students would be able to observe the path in which light travels.
Procedure:
Take a flashlight. Place a cardboard in front of the flashlight. Make a small hole at the centre
of the cardboard. Switch on the flashlight. This activity would give better result when the
surroundings are controlled, i.e., dark.
Observation:
Picture 4
Students would see that light appears to come out from the small hole in a straight line.
These are the rays of light. Each ray carries energy which can be intelligently used to
perform a range of tasks related to health, recreation and disease tasks e.g. physiotherapy
(to relax the tensed muscle fibers/tendons/ligaments), straightening of hair, heating, laser
surgery etc. see picture 5.
Picture 5
Conclusion: Light travels in a straight line.
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17
ACTIVITY 2B
Demonstration:
Take a paper or plastic pipe and a torch. Switch on the torch and ask a student to hold the
pipe straight so that he/she can see the light coming from the torch bulb. Now ask the
student to bend the pipe and repeat the same activity. The student will not be able to see the
light coming from the torch bulb. See picture 6.
Conclusion: This activity shows that light ALWAYS propagates along a straight line.
Picture 6
ACTIVITY 2C : PATH OF LIGHT
Rectilinear propagation of light (demonstration by the teacher)
Procedure:
Picture 7
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Science
Take three equal sized square black (hard paper) sheets. Put all the three sheets exactly one
over the other and with the help of a long nail punch a hole through all of them. Place the
papers one after the other in a straight line with a separation of about 3 cm . On one end of
this set-up place a lighted candle. Students will be able to observe the flame of the candle
from the other side of this set up of three sheets. Now shift the middle paper a little and ask
the student to see the flame again. The flame will not be visible.
Conclusion: This demonstration proves that light propagates along a straight path.
Some everyday phenomena which suggest that light always propagates along a straight
path.
F
Passage of sunlight through the ventilator in a dark room.
F
Beam of a search light used in lighthouses or airports, night sports.
F
Light from the car's headlight. See picture 8.
Picture 8
F
Light coming out of a laser torch . See picture 9.
Picture 9
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4. CLASSIFICATION OF OBJECTS
Luminous and Non Luminous Objects
Light travels from its source to the objects. The source is also called Luminous.
Luminous bodies or objects are those that emit light of their own. For example, the sun,
stars and fire are luminous bodies. Non-luminous bodies are those that do not emit light of
their own. For example books, tables and chairs , are non-luminous bodies.
Sun- A luminous object
Book- A non- luminous object
The following activity can be taken to differentiate between luminous and non-luminous
objects.
ACTIVITY 3 : LUMINOUS AND NON LUMINOUS OBJECTS
Learning outcome: The students will be able to learn that there are two kinds of objects in
nature: Luminous and non luminous.
Procedure:
Switch off all the lights and shut the doors and windows so that the room becomes dark.
Nothing is visible.
Now switch one light. What happened? Can we see each other? Can we see the things
around us? Yes, we can. This is because the Light emitted from the bulb enables us to see
things around us, including the chairs, tables and the rest of the things in the class.
Again, switch off the light. Now, everything around us becomes invisible.
Conclusion: A glowing bulb, which is giving light, is an example of a luminous object
whereas a chair is an example of a non luminous object.
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Science
FORMATIVE ASSESSMENT 1
Mark the most appropriate option1)
2)
Light is a form of energy that is produced by a
1.
Transparent object
2.
Luminous object
3.
Non-luminous object
4.
Opaque object
An example of a non-luminous object is
1.
a meteorite
2.
the sun
3.
an electric bulb
4.
a candle
Test your knowledge1.
Write two statements related to luminous objects?
2.
Give two examples each of (i) natural (ii) man-made luminous objects?
3.
Both Sun and a bulb are luminous objects. In what way are they different from
each other.
4.
Is Earth a luminous or a non-luminous object? Give reasons.
There are two type of luminous sources:
1.
Natural
2.
Man-made
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1.
Natural luminous sources
Natural light sources includes sun, glowing rocks (lava from volcanoes) and flames.
Some plants and animals like glow worms and some deep sea fish, give off light of
their own.
Lava from volcanoes
2.
Man-made(artificial) luminous sources
There are a lot of man made sources of light, some of them are: candles, light bulbs,
CFL's, tube-lights, kerosene lamps etc.
Light bulbs-Man-made luminous source
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Science
WORKSHEET 1
Classify the following objects as natural and artificial source of light.
Objects
Pictures
Luminous/ Non-luminous
Bulb
Stars
Glow Fish
Candle
Street light
Sun
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Planets
Fireflies
Torch
Candle
House
Tree
Suggested activities / processesF
Showing small video clips on luminous and non luminous objects
F
Showing a small video clip of fireworks and lightning and thunder (to explain the
speed of light and its comparison to speed of sound).
F
Heating an iron rod will make the rod red hot
F
Explaining rectilinear propagation of light through a practical experiment with
the help of a candle and two straws (one straight and one bent).
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Science
Transparent, Translucent and Opaque materials
ACTIVITY 4 : CLASSIFICATION OF MATERIAL
Precontent
Learning outcome: Students will be able to understand that there are three kinds of
material; Transparent, Translucent and Opaque in terms of their behavior towards light.
Transparent
Translucent
Opaque
Procedure:
Let us take these three objects (glass tumbler, colored glass and wooden block).
Keep them on the table. Now place a pencil box on the other side of these objects.
What do you observe?
In case of glass tumbler, the pencil box on the other side can be seen clearly.
F
In case of colored glass ,the pencil box on the other side, is not seen very clearly.
F
In the third case, the pencil box is not at all seen from the other side of the wooden
F
block.
Conclusion: We say that , the first object is transparent, the second object is translucent
and the third one is opaque.
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A transparent object is one which allows all of the light to pass through it. Things like glass,
clear water are transparent.
A translucent object is one which allows only some of the light to pass selectively through
it. Things like tissue paper, wax paper, muddy water, cloth and paper are all translucent.
An opaque object is one which does not allow light to pass through it . Objects like wood,
paint, metal sheets and books are opaque.
Wooden pot
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Metal sheet
Science
Diamond is not a luminous body even though we see it as a shinning object. It is a
transparent object which allows light to pass through it but after some reflection (about
which we will learn in the later part of the chapter).
Suggested activities / processesF
Hold a pencil box, a butter paper, a glass sheet and a lunch box one by one in front
of the eyes of the students and ask them to look at a source of light through them.
Now ask the students to observe the light source, and note down their
observations.
F
Close your eyes while looking towards bright sunshine.Now cover the eyes with
your palm,still keeping them closed. Do you notice any difference? On the basis of
this experience , state whether your eyelids are transparent , translucent or
opaque.
F
Apply some oil on a white sheet of paper. Ask the students to hold it in front of
their eyes. Can they see through it? Put a torch light on one side of the paper and
ask the students to observe it from the other side. They will find that some light
passes through it. Repeat the same with a tracing paper and a brown or a dark
colour paper : Note the observations. What can you conclude from it.
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FORMATIVE ASSESSMENT 2
Mark the most appropriate option1.
2.
3.
4.
28
Butter paper is an example of _______ object.
1.
A transparent
2.
A translucent
3.
An opaque
4.
A luminous
Objects, that allow only some light to pass through them, are considered as
__________.
1.
Opaque
2.
luminous
3.
Transparent
4.
Translucent
Cloud is an example of______________object.
1.
an opaque
2.
a luminous
3.
a transparent
4.
a translucent
Translucent Objects
1.
Allow all light to pass through them.
2.
Do not allow any light to pass through them.
3.
Allow some light to pass through them.
4.
Reflect all light falling on them.
Science
5.
An opaque object
1.
allows all light falling on it to pass through it.
2.
does not allow any light to pass through it
3.
allows some light to pass through it
4.
reflects all light falling on it.
2.
Suggest a way to make an opaque paper translucent.
3.
Air is____________. (Transparent /translucent/opaque). Give reasons.
4.
State the main difference between opaque and transparent materials.
6. LIGHT AND SHADOW FORMATION
Many objects do not allow light to pass through them at all. Such objects are called opaque.
When light from a source passes through an opaque object, a shadow is formed. This is
shown in the following diagrams where the path of light is shown by straight lines with an
arrow. The rays shown are sample rays (from the source)and going from the edges of the
object causing the shadow. The formation of shadows, is a reconfirmation of the
observation that light ordinarily propagates along in straight path.
Ray diagrams
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A shadow is actually a region where there is absence of light. The size of the shadow in the
diagrams depends on the distance of the object from the source of light. The drawing of the
rays of light, or ray diagrams as they are known, shows that the closer the object to the light
source, the larger the shadow.
Shadow of a man
Shadow of a globe
Shadows made by the Sun
The Sun is a natural source of light. It seems to move across the sky during the day.
Different (opaque) objects cast (make) their longest shadows in sunlight , at the beginning
and at the end of the day i.e during the sunrise and the sunset.These are the times when the
Sun is lowest/farthest in the sky from the observer/object as shown in the figure below.
The (opaque) objects cast their shortest shadows at midday, i.e., when the Sun is directly
above the head in the sky and is at the shortest distance from the objects as shown in the
figure below (see).
Shadow at sunrise or Sunset (longest)
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Shadow at midday (shortest)
Science
ACTIVITY 5 : MEASURING SHADOW AT DIFFERENT TIMES
Learning outcome: Student would be able to observe that the length of the shadow of an
object, in daylight, is different at different times of the day.
Procedure: Fix a stick straight on the school ground field away from the school building
and the trees.
Observe the length of the shadow of the stick at different times of the day and note down
the observation in the table belowObservation:
Time
Side of the shadow
Length of the shadow
7:30 am
10:30 am
12:00 pm
2:30 pm
5:00 pm
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Parts of a shadow
A shadow has two parts; they are called the Umbra and the Penumbra The completely
dark part of the shadow is called the Umbra. The part of the shadow where it appears
light(i.e.,where some light is able to reach) is called the Penumbra.
Place a lamp close to a mug and observe its shadow on a table. Notice that the shadow
formed has two parts. The darker part of the shadow, is the "umbra" and the lighter part is
the "penumbra".
Conditions necessary for the formation of the shadowF
A light source
F
An (opaque) object
F
A screen or a wall (Any surface)
Shadow formation: The size of a shadow varies depending on the distance between the
source and the object as well as the distance between the object and the screen.
If the screen is moved closer to the obstacle, the size of the shadow decreases and viceversa.
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Science
A. DIAGRAMMATIC PRESENTATION OF SHADOW:
(i)
Small source with a large obstacle
(ii) Large source with large obstacle
If the screen is moved away from the obstacle , then both umbra and penumbra would
increase in size.
(iii) Large source with a small obstacle.
If the screen is moved away from the obstacle , then you will see that umbra has been
reduced to a point and the penumbra has increased in size. If the screen is moved further
away , then you will observe only penumbra which is large and faint while umbra is absent
from the shadow.
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ACTIVITY 6 : CHANGING SIZE OF A SHADOW
Learning outcome: Students would be able to observe that the size of the shadow of an
object on the wall, depends on its location with respect to the light source and the wall.
Materials required:
Flashlight, cardboard, screen (or wall) and a ball.
Procedure: Make a small hole in the cardboard and place it in front of the flashlight. Hold
the ball at certain distance from the flashlight. Switch on the flashlight and observe the
shadow on the wall. Move the source of light and the ball together away from the screen
(wall). Note down the observation. Now, instead of moving the ball and the flashlight
together, increase the distance between the flashlight and the ball. Note down the
observation again.
Observation:
Position of the light
source
Position of the
object
Size and shape of the shadow
on the screen
ConclusionIf an object is moved closer to the light source, the shadow gets bigger.
F
If an object is moved farther away from the light source, the shadow
F
gets smaller.
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Science
ACTIVITY 7 : MEASUREMENT OF SHADOWS ON THE WALL
Learning Outcomes:
F
The student will be able to observe changes in the location, shape, and size of a
shadow when an object is placed in different positions with respect to the light
source and screen(wall)
Plan a procedure and make observations to determine changes in a shadow's
F
location, shape, and size when an object is placed in different positions with
respect to a light source and screen.
Materials:
Table lamp.
Plain wall.
Chart paper taped to wall for sketching shadows.
Ruler or measuring tape, pencil and record sheet.
Procedure:
1.
Fix a screen or a chart paper to the wall where the shadows will be cast.
2.
Place the table lamp few meters away from the wall.
3.
Turn off the lights in the room, and adjust the lamp so that the paper is uniformly
lit.
4.
Cast shadows on the paper using your arms, head and body and some
other(opaque) objects. Try changing your distance from the light and observe any
changes in the shadows.
5.
Sketch shadows for different positions of different objects. Make sure you
observe and measure the grey area in the shadow.
Reflection:
1.
"Become the wall" by standing with your back to the paper facing the light.
Record what you see as your partner moves back and forth between you and the
light, the types of shadow that falls on you. Change places for your partner to
observe.
2.
Write down your observations about how shadows change location, shape, and
size.
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35
ACTIVITY 8 : THE CAUSE OF SHADOW FORMATION
Learning outcome: The student will be able to understand formation of a shadow.
Materials: Small torch, Big torch, Different objects, Candle and Pencil.
When we put any (opaque) object in front of a light source, a shadow of that object gets
formed. The closer the object is to the source of the light, the more light it blocks out and
bigger is the shadow. If the object is far away, it does not block out much light, and so the
shadow is smaller.
Procedure:
1.
Put on the light.
2.
Keep the object in between the light source and wall.
3.
First, keep the object near to the light source and observe the shape of the shadow
of that particular object.
4.
Next, move and push the object towards the wall, moving it away from the light
source.
5.
Again observe the size of the shadow of the object.
Observation:
Observation is done on the basis of the object position and the various sizes of the shadow.
Position of the object
36
Size and shape of the shadow on the screen
Science
ConclusionF
If an object is moved closer to the light source, the shadow gets bigger.
F
If an object is moved farther away from the light source, the shadow gets smaller.
ACTIVITY 9 : SHADOW FORMATION -DISTANCE BETWEEN
LIGHTAND OBJECT
Procedure:
1.
Take one candle and light it. Put it on the table.
2.
Put a sharp pencil on the table in between the candle and wall. Keep the sharp end
of the pencil placed at the top. Observe the shadow of the pencil on the wall.
3.
Move the pencil towards the wall. Position it to be in the middle of the wall and
candle. Observe the shadow of the pencil on the wall.
4.
Again move the pencil near towards the wall. Again observe the shadow of the
pencil on the wall.
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37
Observation:
Sl. No.
Position of pencil
1
Near to the candle
2
In the middle of the candle and wall
3
Near to the wall
Shadow formation
Conclusion:
When the object is closer to the light it blocks out more light and therefore its shadow is
bigger in size. If the object is farther away, it does not block out much light, and so the
shadow is smaller.
Shadow formation in nature (Eclipses)
The passage of one celestial body in front of another, resulting in blocking of the light(from
the luminous body) by the second body (e.g. blocking of the light of the sun by the moon, or
that of one star by the other) is called an eclipse.
An eclipse, of sun or the moon , can occur whenever the three (heavenly!) bodies: the Sun,
the Earth and the Moon come in a straight line.
Formation of the Eclipses
a)
Solar Eclipse-
An eclipse of the sun occurs when the moon, revolving in its orbit around the earth, comes
between the sun and the earth. The moon blocks the light of the sun and a shadow of the
moon is cast over the earth's surface. This can only happen during a new moon, when the
Sun and Moon are in a straight line.
During a solar eclipse, the moon actually casts two types of shadows towards the earth.
One shadow shaped like a cone is called the umbra.
The second shadow is called the penumbra. This spreads out as it reaches the earth. The
penumbra is thus spread over a large area.
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Science
The part of the earth which lies in the umbra region of the moon's shadow experiences a
total solar eclipse and the part of the earth lying in the penumbra of the moon's shadow
experiences a partial solar eclipse.
Total eclipse
b) Lunar EclipseAn eclipse of the Moon (or lunar eclipse) occurs when the sun , the earth and the moon are
in a straight line, with the earth situated in between the sun and the moon.A lunar eclipse
takes place on a full moon. The type and length of a lunar eclipse depends upon the Moon's
location.
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39
The Geometry of a Lunar Eclipse
Teaching Suggestions, Activities and Demonstrations
F
Distinguish between a solar eclipse and a lunar eclipse. Set up a demonstration to
allow students to visualize these two phenomena.
F
Perform an activity to observe the umbra and penumbral regions of a shadow.
Transfer these ideas to explain what happens during an eclipse.
F
Opaque objects produce the darkest shadows. One activity that could be done is
to set up a bright light in the room, getting the rest of the room as dark as possible.
The children should place objects in front of the light to discover which objects
create shadows and which ones block light most completely.
F
By folding hands in different patterns in a dark room, one can make different
types of shadows on the wall. These may look like the head of a duck or a dog and
shadow that resemble other animals or shapes.
F
Light a candle and suspend a tennis ball at a little distance from it. Observe its
shadow on the wall. Move the ball a little and change its distance from the burning
candle . Observe the changes in the size of its shadow.
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Science
Fun with shadows:
1.
Put on a shadow play, using a sheet as your screen.
2.
Try measuring your partner's shadow outdoors at different times of a sunny day,
to see how the position of the sun affects the size of a shadow.
3.
Enact a play using different shadows on a screen.
7. MIRRORS AND REFLECTION
An image is a reflection of an object in the mirror. Mirrors generally change the direction of
light which falls (incident) on them.
Plane mirror
image in a mirror
In the above picture we can see an image of a pot, looking exactly like the pot, is at same
distance from the mirror as the real pot is from the mirror. This image however, is not real.
When an image is formed on a screen or a wall it is called a real image. How is this image
formed? It follows the principle of reflection.
Lateral Inversion:
When an image of an object is formed in a plane mirror, some reversal of position takes
place.
The reversal experienced by an image formed in a plane (flat) mirror is side ways. In it left
and right sides appear to move from one side over to the other. The side to side reversal of
the image and the object is called Lateral Inversion.
For example, a hair parting that appears to be on the left when viewed in a mirror is seen by
everyone else to be on the right.
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41
Ambulance as seen through a mirror
The principal of lateral inversion is used by the ambulance services. The laterally inverted
image of the word AMBULANCE is placed in the front of the vehicle carrying the patients.
It can be read clearly when seen from the rear mirror of the car ahead of the ambulance and
give passage to the van. As health is considered a priority of life, this practice is universally
accepted in east & west parts of the world.
8. LIGHT AND ITS APPLICATIONS
2)
Periscope
Periscope
periscope is an optical device, which allows an observer to see things, that are beyond a
person's direct line of sight. One of the classical uses of a periscope is made in submarines.
Periscopes consist of a long tube, which can contain mirrors. One end of the mirror
captures the image and bends or reflects it so that it can travel down the tube to hit the
mirror at the other side. This bends the rays again so that they can meet the eye of the
viewer.
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Science
A periscope works by using two mirrors to reflect light from one place to another. It uses
two mirrors at 45 degree angles to the direction of the incident light. The light gets
reflected from one mirror to the other mirror and then reaches the person's eye as shown in
the figure below. (see)
Working of a periscope
Uses
F
People can use a periscope to see things located above their current position
allowing them to stay concealed and protected behind an armor or a wall,
F
Periscopes can also be used to look underground and around corners.
F
It is used to see what is going on at sea level from the submarine, which can stay
safely submerged under the water.
F
Periscopes are widely used in the military and also in other fields, like medicine
and hunting.
3)
Pinhole Camera
Pinhole camera, also known as camera obscure, or "dark chamber", is a simple device in the
shape of a closed box or chamber. In one of its sides there is a small hole near its center. Due
to the rectilinear propagation of light ,this hole can create an image of the outside space on
the opposite side of the box.
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43
It is, therefore, one of the applications of rectilinear propagation of light.
The image in the pinhole camera is created on the basis of the rectilinear propagation of
light as shown in the figures below. Each point on the surface of a luminous object emits
rays of light in all directions. The hole lets through a certain number of these rays, which
continue on their course until they meet the opposite side of the box where they produce a
reverse image of the object.
Ray passing through P
If a ray (straight line) starts from top of the object (P) and passes through the pin hole in the
middle, then it will meet the right hand side of the screen at the bottom .
Thus, top of the object will become the bottom of the image on the screen on right.
Similarly, a ray, starting from bottom of the object, and passing through the pinhole in the
middle will meet the right hand side of the screen at the top. The bottom of the object will
thus become the top of the image. Hence the image formed is a real and inverted image.
(When the image gets formed on a screen, it is known as a real image).
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Science
Making of pinhole camera using a box
F
Make a hole in one side of a box made of a material which does not let light in.
F
Place a thin piece of metal or a tin can with a tiny hole over the opening. On the
outside of the box stick a strip of black tape over the opening, which acts as the
release.
F
Next, in a dark room, attach a piece of film or photographic paper onto the
opposite side and the camera is ready.
Teaching Suggestions, Activities and Demonstrations
F
Suggest practical applications, which illustrate the lateral inversion of an image in
a plane mirror, like making an L on a paper and asking the students to hold and
identify the letter.
F
Three mirrors placed at an acute angle to one an other produce a kaleidoscopic
effect, with formation of multiple images.
F
Making a periscope using mirrors and cardboard.
Science
45
WORKSHEET 3
1.
How does reflection of light, from smooth and rough surfaces differ from each other?
2.
Object A reflects more than object B.
Therefore, object A is likely to be __________ object B.
Made of the same material as
b.
Smoother than
c.
Just as smooth as
d.
Rougher than
If a capital letter R is seen in an ordinary plane mirror, what does it look like?
a.
b.
c.
d.
4.
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R
R
R
R
3.
a.
When light falls on the following objects which among them would show the darkest
shadows. Why?
a.
a sheet of thin tissue paper
b.
a glass window
c.
a wooden chopping board
d.
a water in a glass.
5.
Name the process due to which it is possible for us to see the objects itself and not their
image.
6.
The inversion of an image, from left to right side, as seen in a plane mirror is called
_____________ inversion.
7.
Show the working of a periscope with a ray diagram.
Science
Points to remember
Luminous objects emit light. Non luminous objects do not emit light of their own.
F
We see them by the light they reflect.
Light propagates along a straight path. It can spread out in all directions from a
F
luminous source.
Objects, which allow light to pass through them (almost completely), are called
F
transparent.
Objects, which allow only some light to pass through them are called translucent.
F
Objects, which do not allow (almost any) light to pass through them, are called
F
opaque.
A ray is a thin straight line used to depict the propagation of light energy. A
F
collection of a large number of rays is called a beam of light.
A shadow is a dark patch behind an object where light is blocked by an
F
(opaque)object.
The shape and the size of the shadow depend on the angle and distance between
F
the light source and the object. As distance between them increases the shadow
becomes smaller. The size of the shadow on a screen increases as the distance
between the object and the screen increases.
Shadow is generally black in colour while images can be coloured.
F
When the moon's shadow falls on the earth we have a solar eclipse. When the
F
earth's shadow falls on the moon, we have a lunar eclipse.
The bouncing of light off a surface is called reflection.
F
Tasks
Students can collect information on various types of Solar and Lunar Eclipses.
F
Students can also do some research on the properties and composition of
F
sunlight.
Science
47
SUMMATIVE ASSESSMENT
Q1. Choose the correct option in each of the following:
1.
2.
3.
4)
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Shadows form because
a.
Opaque objects reflect light.
b.
Opaque objects do not allow light to pass through them.
c.
Light propagates in one direction from the source.
d.
Light is allowed to pass through the object.
The paint behind a plane mirror
a.
Protects the glass.
b.
Reflects the light.
c.
Stops the light from passing through.
d.
Protects the metallic coating of the mirror
Which of the following statements is true?
a.
Moon is a luminous object and reflects light of the sun towards the earth.
b.
Moon is a non luminous object and reflects light of the sun towards the earth.
c.
Moon is non luminous and not reflect any light of the Sun towards the earth.
d.
Moon gives out its own light in the night and reflects sunlight during the day.
The umbra portion of the shadow
a.
does not receive no light at all.
b.
receives light from the top of the source.
c.
receives light from the middle portions of source.
d.
receives light from the bottom of the source.
Science
5.
6.
7.
Why do shadows made by the Sun change in size in day time?
a.
Because the weather changes.
b.
Because the objects keep moving.
c.
Because the Sun appears to move across the sky each day.
d.
Because the amount of light, emitted by the Sun, keeps on changing.
Shadows made by the Sun
a.
are shortest in the morning, when the Sun is rising.
b.
are shortest at midday, when the Sun is directly overhead.
c.
are shortest in the evening, when the Sun is setting.
d.
do not change their size throughout the day.
The diagram shows a child using a periscope to look at an object on the other side of a
wall.
Which diagram shows a correctly drawn ray of light from the object?
Science
49
8.
A boy did the following experiment.
He kept a wooden cube in front of a screen. He had three torches with him.
Without changing the position of the cube and the screen, he placed the other two
torches one after the other, in the position of torch 1, and saw the shadow.
Which torch will make the largest(umbra) shadow on the screen?
9.
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1.
Torch 1
2.
Torch 2
3.
Torch 3
4.
The size of the shadow will be the same for all the three torches.
When an object moves closer to a source of light, its shadowa.
gets bigger.
b.
gets smaller.
c.
stays the same size.
d.
increases or decreases depending on the material of the object.
Science
10. Answer the following questions based on the figure below-
(i) What are the various sources of light here in the above figure?
(ii) Explain why no sunlight enters into the cave chamber?
(iii) Which of the following is not a source of light?
a.
Candle
b.
Caver's lamp
c.
Mirror
d.
Sun
(iv) If his lamp stopped working, what would the caver be able to see?
a.
A mirror
b.
The tunnel to the cave
c.
The walls of the cave
d.
Nothing
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51
11. Study the first pair given and complete the second:
(i)
Objects that do not allow light to pass through: opaque:: objects that allow light to
pass partially: ____________.
(ii) Rays of light spreading out from the source: divergent rays: rays of light coming
together to meet at a point:______________.
(iii) Earth in between the sun and the moon: Lunar eclipse: Moon in between the earth
and the sun: _______________________
12. While you are looking at your image in a large plane mirror, when you touch it with
your left hand it appears as if your image has touched it with its right hand. Why?
13. The diagram given below shows the formation of shadow by an opaque object. Study
it carefully to answer the following :
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Science
i)
What happens when the distance between the light source and the object
increases?
ii)
What happens when the distance between the object and the screen increases?
14. A few details about the puppet show are given. A screen is placed and light is made to
fall onto the screen from behind. Puppets are held between the light and screen and are
moved according to the story narrated. Based on this, Answer (a) and (b).
a. The screen in the above case was made of the cloth. Which other material could be
used instead of cloth?
b.
Science
(i)
A mirror as it would allow the light to bounce back.
(ii)
A large transparent plastic sheet as it allows the light to pass through it.
(iii)
A sheet of thick paper as it would not allow light to pass through it and the
shadow would be sharp.
(iv)
A large sheet of ordinary paper as it would allow light to pass through it.
How would the shadow be when the puppets are held close to the screen?
(i)
The shadow will be smaller and sharper.
(ii)
The shadow will be bigger in size and sharper.
(iii)
The shadow will be bigger in size but not sharper.
(iv)
The shadow will be smaller in size but not sharper.
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15. Identify the position of the source casting the shadow
16.) What is the differences between a black coloured object and the dark shadow?
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Science
RUBRICS
FOR ASSESSMENT FOR LEARNING
Parameter ability
Indicator
Beginning
(1)
Partially
Proficient
(2)
Proficient
(3)
Exemplary
(4)
Define luminous and
non luminous objects
Explain rectilinear
propagation of light
and illustrate the
phenomenon from
daily life events.
Differentiate between
transparent,
translucent and
opaque objects with
an illustration.
Illustrate the
formation of shadow
with the help of an
activity
Explain the formation
of a pin hole camera
Explain the
construction and
working of a
periscope
Science
55
Resources: Suggested WeblinksF
www.icteachers.co.uk/children/sats/light.htm
F
http://www.tutorvista.com/content/physics/physics-iii/physics
F
http://www.practicalphysics.org/go/Default.html
F
http://lgfl.skoool.co.uk/content/keystage3/Physics
F
www.yteach.co.uk/.../Acetate_LED_Detonator_Luminous_Lunar_Opaque
_Sensor_Solar_Umbra_light_sun_t_page_2.html
F
http://www.sasked.gov.sk.ca/docs/physics/u220phy.html
F
www.wikipedia.com
F
www.answer.com
F
www.brainpop.com
F
www.trachersnet.com
F
Library.thinkquest.org
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