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Ray Optics and Optical Instruments · Question 68

AIPMT 2003MCQMedium📈 Topic in 25% papers+4−1
1

An equiconvex lens is cut into two halves along (i) XOX′ and (ii) YOY′ as shown in the figure. Let f, f', f'' be the focal lengths of the complete lens, of each half in case (i), and of each half in case (ii), respectively. Choose the correct statement from the following [figure]

  1. f' = f, f'' = 2f
  2. f' = 2f, f'' = f
  3. f' = f, f'' = f
  4. f' = 2f, f'' = 2f

Answer

(1) f' = f, f'' = 2f

Solution

For the equiconvex lens (radii R and −R), by the lens maker's formula:

1f = ( - 1) ( 1R + 1R ) = 2( - 1)R

Case (i): cut along XOX′ (the principal axis). Each half still has both curved surfaces of radius R.

⇒ 1f' = 2( - 1)R ⇒ f' = f (only the amount of light, i.e. intensity, is halved)

Case (ii): cut along YOY′ (perpendicular to the axis). Each half is plano-convex (R2 = ).

⇒ 1f'' = ( - 1) ( 1R - 1 ) = - 1R

⇒ f'' = 2f

Answer: (1)

AIPMT 2003

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2

A convex lens is dipped in a liquid whose refractive index is equal to the refractive index of the lens. Then its focal length will

  1. become zero
  2. become infinite
  3. become small, but non-zero
  4. remain unchanged
AIPMT 2003
3

A bulb is located on a wall. Its image of the same size is to be obtained on a parallel wall with the help of a convex lens. The lens is placed at a distance d ahead of the second wall, then the required focal length will be

  1. only d4
  2. only d2
  3. more than d4 but less than d2
  4. less than d4
AIPMT 2002
4

For the given incident ray as shown in the figure, for total internal reflection of this ray, the required refractive index of the prism will be [figure]

  1. 3+12
  2. 2+12
  3. 32
  4. 76
AIPMT 2002
5

Optical fibres are based on

  1. total internal reflection
  2. less scattering
  3. refraction
  4. less absorption coefficient
AIPMT 2001
6

A ray of light travelling in air has wavelength , frequency n, velocity v and intensity I. If this ray enters into water then these parameters are ', n', v' and I' respectively. Which relation is correct from following?

  1. = '
  2. n = n'
  3. v = v'
  4. I = I'
AIPMT 2001
7

A disc is placed on a surface of pond which has refractive index 5/3. A source of light is placed 4 m below the surface of liquid. The minimum radius of disc needed so that light is not coming out is

  2. 3 m
  3. 6 m
  4. 4 m
AIPMT 2001
8

A bubble in glass slab ( = 1.5) when viewed from one side appears at 5 cm and 2 cm from other side, then thickness of slab is

  1. 3.75 cm
  2. 3 cm
  3. 10.5 cm
  4. 2.5 cm.
AIPMT 2000
9

A tall man of height 6 feet, wants to see his full image. Then required minimum length of the mirror will be

  1. 12 feet
  2. 3 feet
  3. 6 feet
  4. any length
AIPMT 2000
10

A plano-convex lens ( = 1.5) has radius of curvature 10 cm. It is silvered on its plane surface. Find focal length after silvering

  1. 10 cm
  2. 20 cm
  3. 15 cm
  4. 25 cm
AIPMT 2000
11

Rainbow is formed due to

  1. scattering and refraction
  2. internal reflection and dispersion
  3. reflection only
  4. diffraction and dispersion.
AIPMT 2000

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