Wave Optics — Physics STD 12 Science — Question

A point source of light is placed 4 m below the surface of water of refractive index 5 / 3. The minimum diameter of a disc which should be placed over the source on the surface of water to cut–off all light coming out of water is

(a) 2 m

(b) 6 m

(c) 4 m

(d) 3 m

Demagnetisation of magnets can be done by

(a) Rough handling	(b) Heating
(c) Magnetising in the opposite direction	(d) All the above

A coil having an area  is placed in a magnetic field which changes from  to  in a time interval t. The e.m.f. induced in the coil will be

(a)

(b)

(c)

(d)

Diffraction of light can be explained by the following:

In a semiconductor, which of the following statement is correct?

In any Bohr orbit of the hydrogen atom, the ratio of kinetic energy to potential energy of the electron is

(a) 1/2

(b) 2

(c) -1/2

(d)  -2

The current sensitivity of a moving coil galvanometer can be increased by

(a) Increasing the magnetic field of the permanent magnet

(b) Increasing the area of the deflecting coil

(c) Increasing the number of turns in the coil

(d) a, b, c

Electric lines of force about a negative point charge are:

A charge (-q) and another charge (+Q) are kept at two points A and B respectively. Keeping the charge (+Q) fixed at B, the charge (-q) at A is moved to another point C such that ABC forms an equilateral triangle of side l. The net work done in moving the charge (-q) is

(a)

(b)

(c)

(d) Zero

Glass has refractive index m with respect to air and the critical angle for a ray of light going from glass to air is q. If a ray of light is incident from air on the glass with angle of incidence q, the corresponding angle of refraction is

(a)

(b) 90°

(c)

(d)