Reflection And refraction Test

Result

Reflection And refraction Test - 2

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Question 1
1 / -0

In cold countries, the phenomenon of looming (i.e. ship appears in the sky) takes place, because refractive index of air

A
decreases with height

B
increases with height

C
does not change with height

D
becomes infinity at the surface

Solution

In cold countries, the temperature of the land surface is very less. As we move up, the temperature of the air increases. Hence, the refractive index of the air decreases. So the rays coming from the ship are travelling from the denser medium to the rarer medium and it suffers total internal reflection because of which ship appears in the sky. This phenomenon of optical illusion is called looming.
Question 2
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A student has been given a project to prepare an astronomical telescope. Which two types of lenses does she have to buy?

A
Concave lenses of different focal lengths

B
Convex lenses of same focal length

C
Convex lenses of different focal lengths

D
Concave lenses of same focal lengths

Solution

The astronomical telescope consists of two convex lenses. One is an objective lens of large focal length and an eye-piece of small focal length. Hence, she should select two convex lenses of different focal lengths.
Question 3
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The image of a candle formed by a convex lens is found to be real and inverted. What change would be found in the nature of this image if the lower half of the lens is covered with black paper?

A
Only the upper half of the candle would be found in the image.

B
There would be no change in the image of any kind.

C
The image would now be real and erect at the same location.

D
The image would now be real and erect at the same location but its intensity would be reduced to half.

Solution

The position and the size of the image will remain unaffected but the intensity of the image will be reduced to half as the intensity of the image is proportional to the area. As the lower half of the lens is covered with black paper, so the area through which the light is coming will be reduced to half.