Alternating Current — Physics STD 12 Science — Question

In determining the temperature of a distant star, one makes use of

(a) Kirchhoff's law	(b) Stefan's law
(c) Wien's displacement law	(d) None of these

How many meters of a thin wire are required to design a solenoid of length 1m and L = 1mH? Assume cross-sectional diameter is very small.

The current through choke coil increases form zero to 6A in 0.3 seconds and an induced e.m.f. of 30 V is produced. The inductance of the coil of choke is

(a) 5 H

(b) 2.5 H

(c) 1.5 H

(d) 2 H

Two copper balls, each weighing 10g are kept in air 10 cm apart. If one electron from every  atoms is transferred from one ball to the other, the coulomb force between them is (atomic weight of copper is 63.5)

(a) 2.0

(b) 2.0

(c) 2.0

(d) 2.0

Serious draw back of the semiconductor device is

(a) They cannot be used with high voltage

(b) They pollute the environment

(c) They are costly

(d) They do not last for long time

In a radioactive decay, neither the atomic number nor the mass number changes. Which of the following would be emitted in the decay process

(a) Proton

(b) Neutron

(c) Electron

(d) Photon

The activity of a sample is 64 × 10^–5 Ci. Its half-life is 3 days. The activity will become 5 × 10^–6 Ci after

(a) 12 days

(b) 7 days

(c) 18 days

(d) 21 days

A ray of light incidents on a plane mirror at an angle of 30°.  The deviation produced in the ray is

(a) 30°

(b) 60°

(c) 90°

(d) 120°

In Young's double slit experiment how many maximas can be obtained on a screen (including the central maximum) on both sides of the central fringe if λ = 2000 and d = 7000  

(a) 12

(b) 7

(c) 18

(d) 4

An electron moving to the east in a horizontal plane is deflected towards south by a magnetic field. The direction of this magnetic field is: