Current Electricity — Physics STD 12 Science — Question

A particle moving in a magnetic field increases its velocity, then its radius of the circle

(a) Decreases

(b) Increases

(c) Remains the same

(d) Becomes half

The time period of a bar magnet suspended horizontally in the earth's magnetic field and allowed to oscillate

(a) Is directly proportional to the square root of its mass

(b) Is directly proportional to its pole strength

(c) Is inversely proportional to its magnetic moment

(d) Decreases if the length increases but pole strength remains same

In the given reaction  Radioactive radiations are emitted in the sequence

(a) α, β,γ

(b) β ,α, γ

(c) γ ,α, β

(d) β , γ ,α

Constantan wire is used in making standard resistances because its

(a) Specific resistance is low

(b) Density is high

(c) Temperature coefficient of resistance is negligible

(d) Melting point is high

When a certain length of wire is turned into one circular loop, the magnetic induction at the centre of coil due to some current flowing is  If the same wire is turned into three loops to make a circular coil, the magnetic induction at the center of this coil for the same current will be

(a)

(b) 9

(c) 3

(d) 27

The e.m.f. of a cell is E volts and internal resistance is r ohm. The resistance in external circuit is also r ohm. The p.d. across the cell will be

(a) E/2

(b) 2E

(c) 4E

(d) E/4

The force which makes magnet move:

Figure shows electric field lines in which an electric dipole p is placed as shown. Which of the following statements is correct?

In order to quadruple the resistance of a uniform wire, a part of its length was uniformly stretched till the final length of the entire wire was 1.5 times the original length, the part of the wire was fraction equal to

(a) 1 / 8

(b) 1 / 6

(c) 1 / 10

(d) 1 / 4