HC Verma - Concepts of Physics Part 1

Book: HC Verma - Concepts of Physics Part 1

Chapter: 18. Geometrical Optics

Subject: Physics - Class 11th

Q. No. 15 of Short Answer

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15

Two converging lenses of unequal focal lengths can be used to reduce the aperture of a parallel beam of light without losing the energy of the light. This increase the intensity. Describe how the converging lenses should be placed to do this.

We know that, refraction through a convex lens, leads to a converging beam. So, placing the second convex kens within range of first one’s focus will make the aperture reduced and also won’t lose energy.



Chapter Exercises

Short Answer
Objective I
Objective II
Exercises

More Exercise Questions

1

Is the formula “Real depth/Apparent depth= μ” valid if viewed from a position quite away from a position quite away from the normal?
2

Can you ever have a situation in which a light ray goes un-deviated through a prism?
3

Why does a diamond shine more than a glass piece cut to the same shape?
4

A narrow beam of light passes through a slab obliquely and is then received by an eye9figure 18-Q1). The index of refraction of the material in the slab fluctuates slowly with time. How will it appear to the eye? The twinkling of stars has a similar explanation.
5

Can a plane mirror ever form a real image?
6

If a piece of paper is placed at the position of a virtual image of a strong light source, will the paper burn after sufficient time? What happens if the image is real? What happens if the image is real but the source is virtual?
7

Can a virtual image be photographed by a camera?
8

In motor vehicles, a convex mirror is attached near the driver’s seat to give him the view of the traffic behind. What is the special function of this convex mirror which a plane mirror cannot do?
9

If an object far away from a convex mirror moves towards the mirror, the image also moves. Does it move faster, slower or at the same speed as compared to the object?
10

Suppose you are inside the water in a swimming pool near an edge. A friend is standing on the edge. Do you find your friend taller or shorter than his usual height?
11

The equation of refraction at a spherical surface is


Taking, show that this equation leads to the equation



for refraction at a plane surface.
12

A thin converging lens is formed with one surface convex and the other plane. Does the position of image depend on whether the convex surface or the plane surface faces the object?
13

A single lens is mounted in a tube. A parallel beam enters the tube and emerges out of the tube as a divergent beam. Can you say with certainty that there is a diverging lens in the tube?
14

An air bubble is formed inside water. Does it act as a converging lens or a diverging lens?
15

Two converging lenses of unequal focal lengths can be used to reduce the aperture of a parallel beam of light without losing the energy of the light. This increase the intensity. Describe how the converging lenses should be placed to do this.
16

If a spherical mirror is dipped in water, does its focal length change?
17

If a thin lens is dipped in water, does its focal length change?
18

Can mirrors give rise to chromatic aberration?
19

A laser light is focused by a converging lens. Will there be a significant chromatic aberration?

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