71.

A ray of light passes through an equilateral prism such that an angle of incidence is equal to the angle of emergence and the latter is equal to $\frac{3}{4} \mathrm{th}$ the angle of prism. The angle of deviation is

• 45°

• 39°

• 20°

• 30°

The dispersive power of the material of lens of focal length 20 cm is 0.08. The longitudinal chromatic aberration of the lens is

• 0.08 cm

• 0.08/20 cm

• 1.6 cm

• 0.16 cm

An infinitely long rod lies along the axis of concave mirror of focal length f. The near end of the rod is at a distance x > f from the mirror. Then the length of the image of the rod is

• $\frac{{\mathrm{f}}^2}{\mathrm{x} + \mathrm{f}}$

• $\frac{{\mathrm{f}}^2}{\mathrm{x}}$

• $\frac{{\mathrm{f}}^2}{\mathrm{x} - \mathrm{f}}$

• $\frac{\mathrm{xf}}{\mathrm{x} + \mathrm{f}}$

A beaker containing a liquid appears to be half when it is actually two third full. The refractive index of liquid is

• 7/6

• 6/5

• 4/3

• 5/4

If h₁ and h₂ are the heights of the images in conjugate position of a convex lens, then the height of the object is

• h₁ + h₂

• h₁ − h₂

• h₁/h₂

• $\sqrt{{\mathrm{h}}_1{\mathrm{h}}_2}$

The power of the combination of a convex lens of focal length 50 cm and concave lens of focal length 40 cm is

• + 1 D

• − 1 D

• − 0.5 D

• + 0.5 D

Image formed by a convex lens is virtual and erect when the object is placed

• at F

• between F and the lens

• at 2 F

• beyond 2 F

A dim star of magnitude + 14.5 explodes into a nova of magnitude + 2. The factor by which the brightness of the star has increased is

• 12.5

• 10²

• 10⁵

• 10⁴

If the sun becomes twice as hot

• the output of radiated energy will be eight times larger

• it will radiate predominantly in the infrared

• it will radiate predominantly in the ultraviolet

• the output of the radiated energy will be eight times smaller

A telescope has an objective of focal length 50 cm and an eye-piece of focal length 5 cm. The least distance of distinct vision is 25 cm. The telescope is focussed for distinct vision on a scale 200 cm away. The separation between the objective and the eye-piece is

• 75 cm

• 60 cm

• 71 cm

• 74 cm