Alternating Current — Physics STD 12 Science — Question

The dimensions of electric potential are:

The forbidden energy band gap in conductors, semiconductors and insulators are  and   respectively. The relation among them is

(a)	(b)
(c)	(d)

If n_e and v_d be the number of electrons and drift velocity in a semiconductor. When the temperature is increased

(a) ne increases and vd decreases	(b) ne decreases and vd increases
(c) Both ne and vd increases	(d) Both ne and vd decreases

For total internal reflection to take place, the angle of incidence i and the refractive index μ of the medium must satisfy the inequality

(a)

(b)

(c) sin i <

(d) sin i >

The magnetising field required to be applied in opposite direction to reduce residual magnetism to zero is called:

A unitless quantity:

1. Never has a non-zero dimension.
2. Always has a non-zero dimension.
3. May have a non-zero dimension.
4. Does not exist.

A charge Q is divided into two parts of q  and Q - q. If the coulomb repulsion between them when they are separated is to be maximum, the ratio of   should be

(a) 2

(b) 1/2

(c) 4

(d) 1/4

A thick wire is stretched so that its length become two times. Assuming that there is no change in its density, then what is the ratio of change in resistance of wire to the initial resistance of wire

(a) 2 : 1

(b) 4 : 1

(c) 3 : 1

(d) 1 : 4

V-i graphs for parallel and series combination of two identical resistors are as shown in figure. Which graph represents parallel combination

(a) A

(b) B

(c) A and B both

(d) Neither A nor B

The radius of a wavefront as the waves propagate: