Light: Shadows and Reflections
Explore sources of light, discover how light travels, investigate shadows and reflection, and understand images formed by plane mirrors and pinhole cameras.
Chapter Snapshot
- Objects that produce their own light are called luminous objects.
- Objects that do not produce their own light are called non-luminous objects.
- We can see most non-luminous objects because light reflected from them reaches our eyes.
- Light generally travels in a straight line through a uniform transparent medium.
- Transparent materials allow almost all light to pass through.
- Translucent materials allow only part of the light to pass through.
- Opaque materials block light.
- A shadow forms when an object blocks light from reaching a surface.
- A visible shadow requires a light source, an object and a screen or surface.
- A mirror can change the direction of light. This is called reflection.
- An image formed by a plane mirror is erect, of the same size as the object and laterally inverted.
- A plane-mirror image cannot be obtained on a screen.
- A pinhole camera forms an inverted image on a screen.
- Periscopes and kaleidoscopes use reflection from mirrors.
What You Will Learn
- Identify luminous and non-luminous objects
- Differentiate between natural and artificial sources of light
- Explain how non-luminous objects become visible
- Demonstrate that light generally travels in a straight line
- Classify materials as transparent, translucent or opaque
- Explain how shadows are formed
- Identify the conditions necessary for observing a shadow
- Explain how the size and shape of a shadow can change
- Define reflection of light
- Describe the characteristics of an image formed by a plane mirror
- Explain lateral inversion using everyday examples
- Explain the working principle of a pinhole camera
- Compare an image formed by a plane mirror with one formed by a pinhole camera
- Explain the basic working of a periscope and kaleidoscope
Chapter Overview
Light is all around us.
During the day, the Sun lights our surroundings. At night, we use lamps, LEDs and other artificial sources of light.
But an interesting question arises:
Do all the objects we see produce their own light?
The Moon appears bright, but it does not produce its own visible light. It shines because sunlight falls on it and is reflected towards us.
A book, tree, wall or person is also usually visible because light from a source falls on the object and some of that light reaches our eyes.
Light also produces:
- shadows;
- reflections;
- images;
- fascinating optical effects.
Understanding these observations begins with studying how light behaves.
Detailed Explanation
1. Sources of Light
Look around during the day.
The most important natural source of light for Earth is the Sun.
Other objects can also produce their own light.
Examples include:
- stars;
- lightning;
- fire;
- glowing fireflies;
- electric lamps.
Objects that produce their own light are called luminous objects.
Examples include:
- the Sun;
- stars;
- a burning candle flame;
- an electric bulb that is switched on;
- an LED lamp that is glowing;
- lightning.
2. Non-luminous Objects
Most objects around us do not produce their own visible light.
Examples include:
- books;
- tables;
- trees;
- buildings;
- planets;
- the Moon;
- mirrors.
These are called non-luminous objects.
If non-luminous objects do not produce light, how do we see them?
Light from a luminous source falls on them.
Some of that light is redirected towards our eyes.
Therefore, we are able to see the object.
Luminous vs Non-luminous Objects
| Feature | Luminous Objects | Non-luminous Objects |
|---|---|---|
| Own visible light | Produce or emit light | Do not produce their own visible light |
| Visibility | Can be seen because they emit light | Usually seen when light from another source reaches them and is reflected |
| Examples | Sun, stars, glowing lamp, flame | Moon, book, table, mirror |
Show answer
3. Natural and Artificial Sources of Light
Sources of light can also be grouped according to their origin.
Natural Sources
These occur naturally.
Examples include:
- Sun;
- stars;
- lightning;
- natural fire;
- some living organisms such as fireflies.
Artificial Sources
These are produced or controlled by humans.
Examples include:
- electric bulbs;
- LED lamps;
- torches;
- candles;
- lamps.
4. Does Light Travel in a Straight Line?
Have you noticed sunlight entering a dark room through a narrow opening?
The beam often appears straight.
A torch beam also seems to travel along a straight path.
This can be investigated experimentally.
5. Straight Pipe and Bent Pipe Experiment
Another simple observation supports the same conclusion.
If you look at a light source through a straight hollow tube, you may be able to see it.
If the tube is bent strongly, the source is no longer directly visible through the tube.
Why?
Because light does not normally follow the curved path of the bent tube.
The straight-line travel of light explains:
- shadow formation;
- pinhole-camera images;
- why an object cannot normally be seen around an opaque corner without reflection.
6. What Happens When Light Falls on Different Materials?
Different materials interact with light differently.
Some allow almost all light to pass through.
Some allow only part of it to pass.
Others block light.
This gives us three important groups:
- transparent;
- translucent;
- opaque.
7. Transparent Materials
Examples include:
- clean glass;
- clean water;
- clear transparent plastic;
- air.
8. Translucent Materials
Examples include:
- tracing paper;
- frosted glass;
- thin translucent plastic;
- some fabrics.
9. Opaque Materials
Examples include:
- wood;
- metal;
- cardboard;
- stone;
- thick books.
Transparent, Translucent and Opaque Materials
| Property | Transparent | Translucent | Opaque |
|---|---|---|---|
| Light passing through | Almost all | Only part | Almost none |
| Objects seen through material | Clearly | Not clearly | Cannot normally be seen through |
| Example | Clear glass | Tracing paper | Cardboard |
Show answer
10. Formation of Shadows
Have you seen your shadow on the ground in sunlight?
A shadow is formed because your body blocks part of the light travelling towards the ground.
A shadow is closely connected with the straight-line travel of light.
When an opaque object is placed in the path of light:
- light cannot pass directly through the object;
- a region behind it receives less or no direct light;
- this region appears as a shadow.
11. What Is Needed to Observe a Shadow?
To observe a clear shadow, we normally need:
- a source of light;
- an object in the path of light;
- a screen or surface on which the shadow can be seen.
The screen may be:
- a wall;
- floor;
- ground;
- sheet of paper;
- any suitable surface.
12. Do Only Opaque Objects Form Shadows?
Opaque objects produce the most noticeable dark shadows because they block most of the light.
However:
- translucent objects can produce lighter shadows;
- even some transparent objects can produce faint shadows.
Therefore, the statement:
"Only opaque objects can ever produce shadows"
is too absolute.
Materials and Their Shadows
| Material Type | Light Transmission | Typical Shadow |
|---|---|---|
| Opaque | Blocks most light | Dark and clearly visible |
| Translucent | Allows some light through | Lighter shadow |
| Transparent | Allows almost all light through | Usually very faint or less noticeable |
13. What Determines the Size of a Shadow?
A shadow does not always have the same size as the object.
Its size depends on the positions of:
- light source;
- object;
- screen.
Object Closer to the Light Source
The shadow can become larger.
Object Closer to the Screen
The shadow can become smaller and often sharper.
14. Does the Colour of an Object Determine Shadow Colour?
Suppose you use:
- a red ball;
- a blue ball;
- a green ball.
Their shadows under the same ordinary white-light arrangement still appear dark.
Why?
The shadow is not a coloured copy painted by the object.
It is mainly a region receiving less direct light because the object blocks the light.
15. Shape of Shadows
A shadow can sometimes resemble the outline of the object.
However, its shape can change when:
- the object is rotated;
- the light source moves;
- the screen is tilted;
- the object has a three-dimensional shape.
For example, the same object can create different-looking shadows from different directions.
This is why a shadow does not always reveal the exact shape of a three-dimensional object.
16. Reflection of Light
Now place a plane mirror in sunlight or shine a torch beam onto it.
The light changes direction.
This phenomenon is called reflection.
A smooth, shiny surface can produce noticeable reflection.
Examples include:
- plane mirror;
- polished steel;
- calm water;
- shiny metal surfaces.
17. Plane Mirrors
A mirror with a flat reflecting surface is called a plane mirror.
We use plane mirrors in:
- homes;
- dressing mirrors;
- optical devices;
- shops;
- laboratories;
- periscopes.
When you look into a plane mirror, you see an image of yourself.
18. Characteristics of a Plane-Mirror Image
A plane mirror forms an image with several important properties.
1. The Image Is Erect
An upright image is called erect.
A plane-mirror image is erect.
2. The Image Is the Same Size as the Object
If you hold a pen in front of a plane mirror, its image appears the same size as the pen.
Moving the object closer to or farther from the plane mirror does not make it physically magnified in the way some curved optical systems can.
3. The Image Appears Behind the Mirror
The image seems to be located behind the reflecting surface.
4. The Image Cannot Be Obtained on a Screen
Place a screen behind or in front of an ordinary plane mirror.
You cannot capture the mirror image on that screen.
5. The Image Is Laterally Inverted
The image appears to show a left-right reversal.
Characteristics of a Plane-Mirror Image
| Property | Observation |
|---|---|
| Orientation | Erect |
| Size | Same as the object |
| Position | Appears behind the mirror |
| Screen test | Cannot be obtained on a screen |
| Left-right appearance | Laterally inverted |
Show answer
19. Understanding Lateral Inversion
Stand in front of a plane mirror.
Raise your right hand.
Your image appears to raise the hand on the opposite side.
This effect is called lateral inversion.
An important practical example is the word AMBULANCE being written in a laterally reversed form on the front of many ambulances.
When drivers in front look through their rear-view mirrors, the word can appear in the normal readable orientation.
Lateral inversion = apparent left-right reversal
It does not mean that a plane mirror turns the image upside down.
A plane-mirror image remains erect.
20. Image Distance and Object Distance
When you move closer to a plane mirror, your image also appears closer to the mirror.
When you move farther away, the image appears farther behind the mirror.
At a more advanced level, this behaviour is described using the relationship between object distance and image distance.
For Class 7, focus on the observation:
As the object moves relative to the mirror, the apparent image position changes correspondingly behind the mirror.
21. The Pinhole Camera
Can an image be formed without using a lens or a mirror?
Yes.
A pinhole camera can form an image using only a tiny opening and a screen.
A pinhole camera works because light travels in straight lines.
22. Why Is the Pinhole-Camera Image Inverted?
Consider an upright candle.
Light from the top of the candle travels in straight lines.
Only a narrow portion passes through the pinhole and reaches the lower part of the screen.
Light from the bottom of the candle passes through the pinhole and reaches the upper part of the screen.
The paths cross at the pinhole.
Therefore, the image appears upside down, or inverted.
23. Constructing a Simple Pinhole Camera
24. Plane Mirror Image vs Pinhole-Camera Image
These two image-forming systems behave very differently.
Plane Mirror vs Pinhole Camera
| Feature | Plane Mirror | Pinhole Camera |
|---|---|---|
| Main principle | Reflection | Straight-line travel of light |
| Image orientation | Erect | Inverted |
| Image on screen | Cannot be obtained on a screen | Forms on a screen |
| Lateral inversion | Observed | Not the main characteristic studied |
| Image size | Same size as object | Can depend on arrangement and distances |
25. Periscope
Reflection can be used to see objects that are not directly in our line of sight.
One useful device is the periscope.
A simple periscope can be made using two plane mirrors inside a tube or box.
Light from the object:
- enters the upper opening;
- reflects from the first mirror;
- travels down the tube;
- reflects from the second mirror;
- reaches the observer's eye.
Uses of a Periscope
Periscopes or related optical systems can be used in:
- submarines;
- observation positions;
- certain military vehicles;
- situations where the direct line of sight is blocked.
26. Kaleidoscope
Another fascinating device based on reflection is the kaleidoscope.
A simple kaleidoscope can contain:
- three reflecting strips arranged in a triangular form;
- small coloured objects;
- a translucent end covering.
As the kaleidoscope is rotated, the coloured objects change position.
Their multiple reflections produce new patterns.
27. Reflection Around Us
Reflection is not limited to mirrors.
We see reflected light from many surfaces.
Calm Water
A still water surface can form a recognisable reflection.
Polished Metal
A highly polished metal surface can redirect light strongly.
Ordinary Objects
Even rough objects reflect some light.
However, reflection from rough surfaces is scattered in many directions, so they do not normally produce clear mirror-like images.
28. Shadow vs Reflection vs Image
These terms must not be confused.
Shadow, Reflection and Image
| Term | Meaning | Example |
|---|---|---|
| Shadow | Dark or less illuminated region produced when light is blocked | Shadow of a person on the ground |
| Reflection | Change in direction of light at a reflecting surface | Light redirected by a mirror |
| Image | Optical representation of an object | Your face seen in a plane mirror |
29. Light Pollution
Artificial light is extremely useful.
However, unnecessary or excessive artificial lighting at night can create light pollution.
It may affect:
- visibility of stars;
- nocturnal animals;
- insects;
- energy consumption;
- natural day-night cycles.
Good lighting should:
- provide enough illumination for safety;
- avoid unnecessary brightness;
- be directed where needed;
- be switched off when unnecessary;
- use energy-efficient sources.
Responsible lighting benefits both people and the environment.
30. Shadow Puppetry — Science and Culture
Shadow formation has also been used in art and storytelling for centuries.
In shadow puppetry:
- a light source is placed behind a puppet;
- the puppet blocks the light;
- a shadow appears on a screen;
- movement of the puppet creates animated shadow forms.
India has several traditional shadow-puppetry forms.
This provides a beautiful connection between:
science + art + culture.
Concept Map
Concept Map
Foundation Extension
Exam Focus
Important Exam Areas
- luminous and non-luminous objects;
- natural and artificial sources of light;
- Moon as a non-luminous object;
- straight-line travel of light;
- aligned-hole experiment;
- straight-tube and bent-tube observations;
- transparent, translucent and opaque materials;
- conditions needed for shadow formation;
- shadows formed by different materials;
- effect of source-object-screen positions on shadow size;
- effect of object colour on shadow;
- reflection of light;
- plane mirror;
- image and object;
- characteristics of plane-mirror images;
- erect image;
- lateral inversion;
- inability to obtain a plane-mirror image on a screen;
- pinhole camera;
- inverted image in a pinhole camera;
- comparison of plane-mirror and pinhole-camera images;
- periscope;
- kaleidoscope;
- everyday applications of reflection;
- light pollution and responsible use of artificial light.
Key Terms
Key Terms
Quick Revision
Quick Revision
- A luminous object produces its own visible light.
- A non-luminous object does not produce its own visible light.
- The Sun and stars are luminous.
- The Moon is non-luminous and reflects sunlight.
- Most ordinary objects are seen because reflected light from them enters our eyes.
- Light generally travels in straight lines.
- Transparent materials allow almost all light to pass.
- Translucent materials allow only part of the light to pass.
- Opaque materials block most light.
- A shadow forms when an object blocks light.
- A light source, object and screen or surface are normally required to observe a clear shadow.
- Opaque objects usually form darker shadows.
- Translucent objects can form lighter shadows.
- Some transparent objects can produce faint shadows.
- Shadow size depends on the relative positions of source, object and screen.
- Changing an opaque object's colour does not simply make its shadow the same colour.
- Reflection is the change in direction of light at a reflecting surface.
- A plane mirror has a flat reflecting surface.
- A plane-mirror image is erect.
- A plane-mirror image is the same size as the object.
- A plane-mirror image appears behind the mirror.
- A plane-mirror image cannot be obtained on a screen.
- Plane mirrors produce lateral inversion.
- Lateral inversion is apparent left-right reversal.
- A pinhole camera works because light travels along straight paths.
- A pinhole camera forms an inverted image on a screen.
- A periscope uses repeated reflection to redirect light.
- A kaleidoscope produces patterns using multiple reflections.
- Excessive unnecessary artificial lighting can contribute to light pollution.
Practice Questions
A. Multiple Choice Questions
Which of the following is a luminous object?
A. Moon B. Mirror C. Sun D. Book
View Solution
Correct Answer: C. Sun
The Sun emits its own light.
The Moon is visible mainly because it:
A. produces its own visible light B. reflects sunlight C. absorbs all sunlight D. produces electricity
View Solution
Correct Answer: B. reflects sunlight
The Moon is a non-luminous object.
Which material allows almost all light to pass through it?
A. Opaque B. Transparent C. Translucent D. Metallic only
View Solution
Correct Answer: B. Transparent
Transparent materials allow almost all incident light to pass through.
A clear shadow is normally observed when we have:
A. only an object B. only a screen C. a light source, object and screen D. only a mirror
View Solution
Correct Answer: C. a light source, object and screen
The object blocks light and the screen provides a surface on which the shadow can be observed.
The change in direction of light from a mirror is called:
A. absorption B. reflection C. respiration D. conduction
View Solution
Correct Answer: B. Reflection
A mirror redirects incident light through reflection.
An image formed by a plane mirror is:
A. always upside down B. always smaller than the object C. erect and of the same size as the object D. always obtained on a screen
View Solution
Correct Answer: C. erect and of the same size as the object
A plane-mirror image is erect and the same size as the object.
The apparent left-right reversal in a plane mirror is called:
A. inversion of temperature B. lateral inversion C. shadow formation D. refraction
View Solution
Correct Answer: B. Lateral inversion
Lateral inversion is the apparent interchange of left and right in a plane-mirror image.
A pinhole camera forms an image that is generally:
A. inverted B. always erect C. invisible D. laterally inverted only
View Solution
Correct Answer: A. Inverted
Straight-line travel of light through the pinhole produces an upside-down image on the screen.
B. Very Short Answer Questions
-
What is a luminous object?
-
Give two examples of non-luminous objects.
-
How does the Moon become visible?
-
What is a transparent material?
-
What is an opaque material?
-
Define a shadow.
-
Name the three things generally needed to observe a shadow.
-
What is reflection?
-
What is a plane mirror?
-
What is lateral inversion?
-
What is a pinhole camera?
-
Name one device that uses multiple reflections.
Answers
-
A luminous object is an object that emits its own visible light.
-
Moon and book.
-
The Moon reflects sunlight towards our eyes.
-
A transparent material allows almost all incident light to pass through it.
-
An opaque material blocks most light from passing through it.
-
A shadow is a dark or less illuminated region formed when an object blocks light from reaching a surface.
-
A light source, an object and a screen or surface.
-
Reflection is the change in direction of light when it falls on a reflecting surface.
-
A plane mirror is a mirror with a flat reflecting surface.
-
Lateral inversion is the apparent left-right reversal in a plane-mirror image.
-
A pinhole camera is a simple device in which light passes through a tiny hole and forms an image on a screen.
-
A periscope or kaleidoscope.
C. Short Answer Questions
Explain how an aligned-hole experiment shows that light travels in a straight line.
View Solution
When holes in several cardboard sheets are placed along the same straight line, light from a torch can pass through all the holes and reach a screen.
If one cardboard sheet is moved sideways, the holes are no longer aligned and the light is blocked.
This observation supports the conclusion that light travels along a straight path.
Differentiate between transparent, translucent and opaque materials.
View Solution
Transparent materials allow almost all light to pass through them.
Example: clear glass.
Translucent materials allow only part of the light through.
Example: tracing paper.
Opaque materials block most light.
Example: cardboard.
Why does the size of a shadow change when an object is moved between a torch and a screen?
View Solution
Shadow size depends on the relative positions of:
- light source;
- object;
- screen.
When the object moves closer to a small light source, it blocks a wider spread of light reaching the screen and the shadow generally becomes larger.
When it moves closer to the screen, the shadow generally becomes smaller.
List four properties of an image formed by a plane mirror.
View Solution
A plane-mirror image:
- is erect;
- is the same size as the object;
- appears behind the mirror;
- cannot be obtained on a screen;
- is laterally inverted.
Any four correct properties form a complete answer.
Why is the word AMBULANCE sometimes written in a laterally reversed form on the front of an ambulance?
View Solution
Plane mirrors produce lateral inversion.
When a driver in front sees the reversed writing in a rear-view mirror, the lettering appears in the normal readable orientation.
This helps the driver recognise the ambulance quickly.
Why does a pinhole camera form an inverted image?
View Solution
Light travels in straight lines.
Light from the upper part of an object passes through the pinhole and reaches the lower part of the screen.
Light from the lower part reaches the upper part.
The light paths cross at the pinhole, producing an inverted image.
D. Long Answer Questions
Explain the formation of a shadow and describe the factors affecting its size and appearance.
View Solution
A shadow forms when an object blocks light from reaching a screen or surface.
A clear shadow generally requires:
- a light source;
- an object;
- a screen or surface.
Opaque objects usually produce darker shadows because they block most light.
Translucent materials may produce lighter shadows.
The size and shape of a shadow depend on:
- position of the light source;
- position of the object;
- position of the screen;
- orientation of the object.
Moving an object closer to a small light source generally makes its shadow larger on a fixed screen.
Moving it closer to the screen generally makes the shadow smaller.
The colour of an ordinary opaque object does not simply determine the colour of its shadow.
Describe the characteristics of an image formed by a plane mirror.
View Solution
An image formed by a plane mirror has several important characteristics.
Erect
The image appears upright.
Same Size
The image has the same size as the object.
Appears Behind the Mirror
The image seems to be located behind the reflecting surface.
Cannot Be Obtained on a Screen
A screen cannot capture the ordinary image formed by a plane mirror.
Laterally Inverted
The left side appears as the right side and vice versa.
These characteristics distinguish a plane-mirror image from a shadow and from the image formed by a pinhole camera.
Explain the construction and working of a simple pinhole camera.
View Solution
A simple pinhole camera consists of:
- a closed box;
- a tiny hole on one side;
- a translucent screen on the opposite side.
Light from an illuminated object enters through the pinhole.
Because light travels in straight lines:
- light from the upper part of the object reaches the lower part of the screen;
- light from the lower part reaches the upper part.
The light rays cross at the pinhole.
As a result, an inverted image is formed on the screen.
A pinhole camera therefore demonstrates the straight-line travel of light.
Explain the working principles of a periscope and a kaleidoscope.
View Solution
Periscope
A simple periscope contains two plane mirrors.
Light from an object reflects from the first mirror.
It travels through the instrument and reflects again from the second mirror.
The reflected light then reaches the observer.
Thus, the periscope uses repeated reflection to allow objects outside the normal direct line of sight to be seen.
Kaleidoscope
A kaleidoscope contains several reflecting surfaces, commonly arranged in a triangular form.
Small coloured objects are placed near one end.
Light reflected repeatedly by the mirrors produces many images.
These multiple reflections create changing symmetrical patterns when the kaleidoscope is rotated.
E. Application and HOTS Questions
A student says, "The Moon must be luminous because I can see it glowing brightly." Explain the error.
View Solution
Brightness alone does not prove that an object produces its own light.
The Moon is illuminated by the Sun.
Sunlight falls on the Moon and some of it is reflected towards Earth.
Therefore, the Moon is a non-luminous object.
A torch, an opaque ball and a screen are arranged in a straight line. What happens to the shadow if the ball is moved closer to the torch while the torch and screen remain fixed?
View Solution
The shadow generally becomes larger.
When the ball is closer to the torch, it blocks a larger spread of the diverging light reaching the screen.
Therefore, a larger shadow is formed.
A student can see a candle flame through a straight tube but not after the tube is bent. Which property of light does this demonstrate?
View Solution
It demonstrates the straight-line travel of light.
Light from the flame can travel through the straight tube directly to the eye.
It does not normally follow the strongly curved path of the bent tube.
Why can a plane-mirror image not be called a shadow?
View Solution
A shadow and a mirror image form through different processes.
A shadow forms when light is blocked.
A plane-mirror image forms because light is reflected.
A mirror image can show details of the object and is laterally inverted, whereas a shadow mainly represents a region receiving less light.
Therefore, they are different optical phenomena.
Why might a pinhole camera with a very large hole produce a blurred image?
View Solution
A large opening allows many light rays from different points of the object to reach overlapping regions of the screen.
The light patterns overlap more strongly.
This reduces image sharpness and produces a blurred image.
A small pinhole restricts the light paths and produces a clearer image.
Assertion–Reason
Assertion: The Moon is a non-luminous object.
Reason: The Moon is visible because it reflects light from the Sun.
Choose the correct option:
A. Both Assertion and Reason are true, and Reason correctly explains Assertion. B. Both are true, but Reason does not explain Assertion. C. Assertion is true, but Reason is false. D. Both are false.
View Solution
Correct Answer: A
The Moon does not produce its own visible light. It appears bright because it reflects sunlight.
Assertion: A plane-mirror image is laterally inverted.
Reason: In the mirror image, left and right appear reversed.
Choose the correct option:
A. Both Assertion and Reason are true, and Reason correctly explains Assertion. B. Both are true, but Reason does not explain Assertion. C. Assertion is true, but Reason is false. D. Both are false.
View Solution
Correct Answer: A
The apparent left-right reversal is called lateral inversion.
Assertion: A pinhole camera forms an inverted image.
Reason: Light travels in straight lines and rays from different parts of the object cross at the pinhole.
Choose the correct option:
A. Both Assertion and Reason are true, and Reason correctly explains Assertion. B. Both are true, but Reason does not explain Assertion. C. Assertion is true, but Reason is false. D. Both are false.
View Solution
Correct Answer: A
Straight-line travel causes light from the top and bottom of the object to reach opposite regions of the screen.
Apply Your Learning
Create a Light Investigation Station using safe materials.
Prepare four mini-investigations.
Investigation 1 — Light Path
Use:
- torch;
- three cardboards with holes;
- screen.
Test whether light reaches the screen when the holes are aligned and misaligned.
Investigation 2 — Material Classification
Test:
- transparent plastic;
- tracing paper;
- cardboard.
Classify each as:
- transparent;
- translucent;
- opaque.
Investigation 3 — Shadow Size
Use:
- torch;
- ball;
- wall.
Move the ball closer to:
- torch;
- wall.
Record how its shadow changes.
Investigation 4 — Plane Mirror
Observe:
- image size;
- image orientation;
- lateral inversion;
- whether the image can be captured on paper.
Then prepare a table:
| Investigation | Observation | Scientific Principle | | --------------- | --------------------------- | -------------------- | | Aligned holes | Light reaches screen | Straight-line travel | | Cardboard | Light blocked | Opaque material | | Ball near torch | Larger shadow | Shadow geometry | | Plane mirror | Image appears behind mirror | Reflection |
Common Mistakes to Avoid
Final Chapter Summary
Chapter Summary
- Light allows us to see objects and our surroundings.
- Luminous objects produce their own visible light.
- Non-luminous objects do not produce their own visible light.
- The Sun and stars are luminous, while the Moon is non-luminous.
- The Moon appears bright because it reflects sunlight.
- Most ordinary objects are visible because reflected light enters our eyes.
- Light generally travels along straight paths.
- Aligned-hole and straight-tube activities provide evidence for straight-line travel.
- Transparent materials allow almost all light to pass.
- Translucent materials allow only part of the light to pass.
- Opaque materials block most light.
- A shadow forms when an object blocks light from reaching a surface.
- A light source, object and screen are normally needed to observe a clear shadow.
- Shadow size and shape depend on the positions of the source, object and screen.
- Reflection occurs when a mirror changes the direction of light.
- A plane mirror has a flat reflecting surface.
- A plane-mirror image is erect and the same size as the object.
- A plane-mirror image appears behind the mirror and cannot be obtained on a screen.
- Plane-mirror images show lateral inversion.
- A pinhole camera works because light travels in straight lines.
- A pinhole camera forms an inverted image on a screen.
- A periscope uses repeated reflection to redirect light towards the observer.
- A kaleidoscope uses multiple reflections to produce changing patterns.
- Shadow puppetry applies the science of light and shadows in traditional art.
- Responsible use of artificial lighting can help reduce light pollution.