The length of a vertical pole at the surface of a lake of water $\left(\mu =\frac{4}{3}\right)$ is 24 cm. Then, to an under-water fish just below the water surface, the tip of the pole appears to be:

(1) 18 cm above the surface

(2) 24 cm above the surface

(3) 32 cm above the surface

(4) 36 cm above the surface

A microscope is focused on a coin lying at the bottom of a beaker. The microscope is now raised by 1 cm. To what depth should water be poured into the beaker so that the coin is again in focus?

(The refractive index of water is $\frac{4}{3}$)

(1) 1 cm

(2) 4/3 cm

(3) 3 cm

(4) 4 cm

Two transparent media A and B are separated by a plane boundary. The speed of light in medium A is 2.0 x 10⁸ ms^-1 and in medium B is 2.5 x 10⁸ ms^-1. The critical angle for which a ray of light going from A to B suffers total internal reflection is:

(1) sin^-11/2

(2) sin^-12/5

(3) sin^-14/5

(4) sin^-13/4

Which of the following is the possible application of fibre optics?

(1) Endoscopy

(2) High-speed internet traffic

(3) Radio, TV & Telephone signals

(4) All of these

The least distance between a point object and its real image formed by a convex lens of focal length F is:

(1) 2F

(2) 3F

(3) 4F

(4) Greater than 4F

The plane faces of two identical plano-convex lenses, each having a focal length of 40 cm, are placed against each other to form a usual convex lens. The distance from this lens at which an object must be placed to obtain a real, inverted image with a magnification of '-1' is:

(1) 80 cm

(2) 40 cm

(3) 20 cm

(4) 160 cm

Two thin lenses of focal lengths 20 cm and -20 cm are placed in contact with each other. The combination has a focal length equal to:

(1) Infinite

(2) 50 cm

(3) 60 cm

(4) 10 cm

If in a plano-convex lens, the radius of curvature of the convex surface is 10 cm and the focal length of the lens is 30 cm, the refractive index of the material of the lens will be:

(1) 1.5

(2) 1.66

(3) 1.33

(4) 3

A glass concave lens is placed in a liquid in which it behaves like a convergent lens. If the refractive indices of glass and liquid with respect to air are ${}_a{\mu }_g$ and ${}_a{\mu }_l$ respectively, then

(1) ${}_a{\mu }_g$ = 5${}_a{\mu }_l$

(2) ${}_a{\mu }_g$ > ${}_a{\mu }_l$

(3) ${}_a{\mu }_g$ < ${}_a{\mu }_l$

(4) ${}_a{\mu }_g$ = 2${}_a{\mu }_l$

The diameter of the aperture of a plano-convex lens is 6 cm and its maximum thickness is 3 mm. If the velocity of light in the material of the lens is 2 x 10⁸ m/s, its focal length is (approximately):

(1) 10 cm

(2) 15 cm

(3) 30 cm

(4) 60 cm