Chapter 11: Light

Q12Written answer

Correct the following statements.

i) The colour of the shadow of an object depends on its colour.

ii) Transparent objects allow light to pass through them partially.

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Ans: No. The shadow, whenever formed, is always black in colour or dark. Thus, the colour of the object does not affect the colour of the image.

Ans: Translucent objects are the objects that partially allow light to pass through them. Transparent objects allow light to pass through them completely.

Q13Written answer

Suggest a situation where we obtain more than one shadow of an object at a time.

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Ans: Sometimes light falls on an object from different sources like sun, bulb, etc. at one time, due to which multiple shadows of an object are formed at that moment.

For example, say, there is a football match in which many shadows of a player are being formed at a time. This is because light is falling on him from different sources.

Q14Written answer

On a sunny day, does a bird or an aeroplane flying high in the sky cast its shadow on the ground? Under what circumstances can we see their shadow on the ground?

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Ans: We know that to obtain a shadow the object should be placed near the screen but in the case of a bird or an aeroplane the distance between the object and the ground (that acts as screen) is too much. So, the shadow cannot be seen on the ground to obtain a shadow they must fly at a lower altitude.

Q15Written answer

You are given a transparent glass sheet. Suggest any two ways to make it translucent without breaking it.

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Ans: We can convert a transparent glass into a sheet that is translucent by following these steps-

i) By applying oil or butter on it that makes it partially permeable.

ii) By rubbing it with sand paper and making the sheet of glass rough, that will allow the light to pass partially.

Q16Written answer

A torch is placed at two different positions A and B, one by one, as shown in Fig. $11.9$.

The shape of the shadow obtained in two positions is shown in Fig. $11.10$.

Match the position of the torch and shape of the shadow of the ball.

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Ans: Shadow ‘a’ is formed from position A and shadow ‘b’ is formed from position B.

Size of the shadow ‘a’ is bigger than shadow ‘b’ because in position A ball, torch and screen are in the same line whereas in position B they aren’t in the same line.

Q17Written answer

A student covered a torch with a red cellophane sheet to obtain red light. Using the red light she obtains a shadow of an opaque object. She repeats this activity with green and blue light. Will the colour of the light affect the shadow? Explain.

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Ans: We know that the color of shadow remains always dark or black and the screen color or objects color doesn’t affect the shadows’ color. So, the color of light will not have any effect on the shadow.

Q18Written answer

Is the air around us always transparent? Discuss.

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Ans: We can see buildings, plants etc. because the air around us is usually transparent. But when the air gets polluted it doesn’t remain completely transparent. The smoke, dust particles or smog (fog and smoke together) when mixed with air absorbs the light.

Q19Written answer

Three identical towels of red, blue and green colours are hanging on a clothesline in the sun. What would be the colour of shadows of these towels?

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Ans: When the path of light is obstructed by an object, a dark patch is formed which we call shadow. Hence, if no light can reach the region of shadow, the shadow will appear only black in color. As there is always absence of light, the color of shadow doesn’t depend on the color of the object.

Q20Written answer

Using a pinhole camera a student observes the image of two of his friends, standing in sunlight, wearing yellow and red shirts respectively. What will be the colours of the shirts in the image?

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Ans: Pinhole cameras don't change the color of the image or object. So, the color remains the same as that of the object. We can conclude that the color of shirts will be yellow and red in the image formed too.

Q21Written answer

In Fig. $11.11$, a flower made of thick coloured paper has been pasted on the transparent glass sheet. What will be the shape and colour of shadow seen on the screen?

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Worked solution

Ans: The shadow formed on the screen will be the same shape of the given flower but darker in color.

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