EXERCISES
Fill in Blanks:
1. Stars are luminous objects.
2. Opaque objects form dark shadows. 
3. A Shadow is formed in the opposite direction to the direction of source of light
4. Trees covered with many leaves are natural pin-hole camera.
5. butter paper is a translucent object.
6. Reflection gives rise to image formation.
7. Light travels in a straight line.
B. Multiple choice questions
1. Which one is the natural source of light?
ans. a firefly
2. Which of the following will not form shadow?
ans. clear glass
3.The image formed in a pin-hole camera is
ans. inverted and either smaller or bigger or the same size of the object.
4. Light
ans. All of these.
5. The shadow of an object does not show
ans. Colour of the object
6. a clear shadow can be obtained when there is
ans. opaque body is kept near a light source.
C. Very short answer questions. (one word)
1. One example of luminous object the sun.
2. One example of non-luminous object the moon.
3. The image formed in mirror is literally inverted true.
4. Light can travel through a bent tube false
5. An application of rectilinear propagation of light pin-hole camera.
6. Which one cannot be formed without a screen shadow.
D. Short answer questions.
1. Name two natural sources of light and two man-made sources of light.
ans. Natural sources of light- The sun and the firefly (glow worm)
Man-made sources of light- Electric bulb and gas lamp.
2. How do we see non-luminous objects?
ans. We can see non- luminous objects only when light from a lunous object falls on it and after striking it reaches our eyes.
3. When shadow is formed ?
ans. Shadow is formed when light is obstructed by an opaque object.
4. What are the three necessary conditions to form a shadow?
ans. We need sources of light, an opaque object and a screen to see a shadow.
5. How are the shadow formed by translucent and opaque objects different?
ans. Translucent object allows only a small amount of light to pass through it. For example thin plastic, and butter paper
while i Opaque objects does not allow any light to pass through it. We cannot see other objects through other objects. For example wood, stone.
6. What is reflection of light?
ans. The bouncing back of light after striking a surface is called the reflection of light.
E. Long answer questions.
1. Difference between opaque, transparent and translucent object. Write two examples of each.
ans. Depending upon behaviour towards light,we have three kinds of objects
Opaque: An object is said to be opaque if it does not allow any light to pass through it. We cannot see other objects through an opaque object. For example wood, stone etc.
Transparent: The light passes through transparent object easily For example glass, air
Translucent: The object allows only a small amount of light to pass through it. The other objects cannot be clearly seen through a translucent object. For example thin plastic, and butter paper.
2. How will you make a pin-hole camera? Explain its working.
ans. To make a pin hole camera you require the following things
Scissors, aluminium foil, sticky tape, tracing or other thin paper, a pin, a piece of dark cloth, sticking plasters and a shoe box or similar long cardboard box. Then follow the steps
Step One cut off one end of the box and the lid. Cut a hole two centimeters by two centimeters in the middle in the middle of the other end or follow the steps given in the video.
Step two cut a square of aluminium foil to cover the hole.
Stick it in place with the tape.
Step Three Check the lid and the corners of the box to make sure that they have no other holes. If thee are any cover them with sticking plaster.
Step Four Put the lid back on the box and fix it with sticky tape. Make sure no light can get in.
Step Five Fasten a piece of tracing paper over the open end of the box.
Your PIN-HOLE camera is ready.
(You can watch the video attached to the page to learn how to make it. )
3. Show that light travels in a straight line, with the help of an activity. 
ans. Activity Close all the windows and doors your room and make it dark. Now observe the light entering the room through narrow hole or opening. You will see the path of the light is straight.
Like wise, place a lighted candle on a table. Take a drinking straw. closed one eye and look at the candle frame through the straw from the other eye. You will see flame is seen clearly. Now, bend the straw in the middle and look at the candle flame through the straw. You won't see the flame. 
This prove that light travels in a straight line path.
4. Write characteristics of a shadow.
ans. The main characteristics of shadow are as follows:-
(a) It is always black, not depending on the colours of the object used to make the shadow.
(b). It only shows the shape or outline of the object and not the details.
(c) The size of a shadow varies depending on the distance between the object and the source of light, and the distance between the object and the screen.
(d) The shape of the shadow depends on the shape of the object and the position of the source of light.
5. Differentiate between shadow and image of an object in a mirror.
ans. The differences between the image and the shadow of an object are
(a) The length of the shadow changes with the change in the position of the object with respect to the light sources but the length of image in the mirror always remains same.
(b) The shadow is always black. The image is of the same colour as the object.
(c) The image in the mirror is always inverted. The shadow has no such lateral inversion.
(d) A shadow is formed on a screen. The image in a mirror can only be seen and cannot be formed on a screen.
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