Numerical aperture of an optical fiber is a measure of

light gathering power of the fiber

attenuation of light signals in the fiber

difference between the refractive indices of core and the cladding

A concave glass lens of refractive index 1 . 5 is immersed in carbon di-sulfide (refractive index = 1 . 6 ). Which of the following is true? [ Assume both surfaces of the lens have same radius of curvature = R ]

It will behave as convergent lens with focal length 8 R

It will behave as divergent lens with focal length 8 R

It will behave as convergent lens with focal length 7 . 5 R

It will behave as divergent lens with focal length 7 . 5 R

E M B I B E

Physics Crash Course NEET>Chapter 17 - Ray Optics>Level 2>Q 3

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IMPORTANT

Earn 100

A concave mirror and convex lens both have the same focal length in air. When they are submerged in water, they will have the same focal length.

Reason: The refractive index of water is smaller than the refractive index of air.

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Important Questions on Ray Optics

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Physics Crash Course NEET>Chapter 17 - Ray Optics>Level 2>Q 4

A person wants a real image of his own,

3

times enlarged. Where should he stand in front of a concave mirror of radius of curvature

30 cm ?

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Physics Crash Course NEET>Chapter 17 - Ray Optics>Level 2>Q 5

A candle flame

2 cm

high is placed at distance of

2 m

from a wall. How far from the wall must a concave mirror be placed in order to form an image of the flame

6 cm

high on the wall?

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Physics Crash Course NEET>Chapter 17 - Ray Optics>Level 2>Q 6

To find the focal length of a convex mirror, a student records the following data:

Object pin	Convex Lens	Convex Mirror	Image Pin
22.2 cm	32.2 cm	45.8 cm	71.2 cm

The focal length of the convex lens is

f_{1}

and that of mirror is

f_{2}

. Then taking index correction to be negligibly small,

f_{1}

and

f_{2}

are close to:

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Physics Crash Course NEET>Chapter 17 - Ray Optics>Level 2>Q 7

After reflection, the parallel beam of light appears to come from a point then the type of mirror is

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Physics Crash Course NEET>Chapter 17 - Ray Optics>Level 2>Q 8

In case of reflection from curved surface

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Physics Crash Course NEET>Chapter 17 - Ray Optics>Level 2>Q 9

An object is placed at a distance of

20 cm

from the pole of a concave mirror of focal length

10 cm

. The distance of the image formed is

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Physics Crash Course NEET>Chapter 17 - Ray Optics>Level 2>Q 10

Two plane mirrors are inclined at

70 °

. A ray incident on one mirror at angle

θ

after reflection falls on the second mirror and is reflected from there parallel to the first mirror.

θ

is:

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Physics Crash Course NEET>Chapter 17 - Ray Optics>Level 2>Q 11

A point source of light, $S$ is placed at a distance $L$ in front of the center of plane mirror of width $d$ which is hanging vertically on a wall. A man walks in front of the mirror along a line parallel to the mirror, at a distance $2 L$ as shown below. The distance over which the man can see the image of the light source in the mirror is:

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