A convex lens A of focal length \(20\) cm and a concave lens B of focal length \(5\) cm are kept along the same axis with the distance d between them. If a parallel beam of light falling on \(A\) leaves \(B\) as a parallel beam, then distance \(d\) in cm will be 

1. \(25\)                         

2. \(15\)

3. \(30\)                         

4. \(50\)

A medium shows relation between i and r as shown. If speed of light in the medium is nc then value of n is

(1)   1.5

(2)   2

(3)   2^–1

(4)   3^–1/2

For a concave mirror, if the virtual image is formed, the graph between m and u is of the form :

For a convex lens, the distance of the object is taken on X-axis and the distance of the image is taken on Y-axis, the nature of the graph so obtained is :

(1) Straight line                     

(2) Circle

(3) Parabola                          

(4) Hyperbola

The diameter of a plano-convex lens is 6 cm and thickness at the centre is 3 mm. If the

speed of light in the material of the lens is $2\times {10}^8\raisebox{1ex}{$m$}\!\left/ \!\raisebox{-1ex}{$sec$}\right.$, the focal length of the lens is

1. 15 cm                         

2. 20 cm

3. 30 cm                         

4. 10 cm

Shown in the figure here is a convergent lens placed inside a cell filled with a liquid. The lens has focal length + 20 cm when in air and its material has refractive index 1.50. If the liquid has refractive index 1.60, the focal length of the system is

1. + 80 cm                         

2. – 80 cm

3. – 24 cm                         

4. –160 cm

Which one of the following spherical lenses does not exhibit dispersion? The radii of curvature of the surfaces of the lenses are as given in the diagrams

The size of the image of an object, which is at infinity, as formed by a convex lens of

focal length 30 cm is 2 cm. If a concave lens of focal length 20 cm is placed between the

convex lens and the image is at a distance of 26 cm from the convex lens, calculate the

new size of the image.

1. 1.25 cm                             

2. 2.5 cm

3. 1.05 cm                             

4. 2 cm

An achromatic prism is made by crown glass prism $\left(A_c=19°\right)$ and flint glass prism

$\left(A_F=6°\right)$. If ${}_C\mu _v=1.5$ and ${}_F\mu _v=1.66$, then resultant deviation for red coloured ray will

be

1. 1.04°                     

2. 5°

3. 0.96°                     

4. 13.5°