Electric Charges and Fields — Physics STD 12 Science — Question

The properties of a surface are different from those of the bulk liquid because the surface molecules:

1. Are smaller than other molecules.
2. Acquire charge due to collision from air molecules.
3. Find different type of molecules in their range of influence.
4. Feel a net force in one direction.

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

A circular coil of diameter 7cm has 24 turns of wire carrying current of 0.75A. The magnetic moment of the coil is

(a) 6.9	(b) 2.3
(c)	(d)

Three observers A, B and C measure the speed of light coming from a source to be  and . The observer A moves towards the source, the observer C moves away from the source with the same speed. The observer B stays stationary. the surrounding space is vacuum every where. Then

(a)

(b)

(c)

(d)

1A current flows through an infinitely long straight wire. The magnetic field produced at a point 1 metres away from it is

(a)  2

(b)

(c)  2

(d) 2π

Time period of a freely suspended magnet does not depend upon

(a) Length of the magnet

(b) Pole strength of the magnet

(c) Horizontal component of earth's magnetic field

(d) Length of the suspension thread

The radius of hydrogen atom in its ground state is 5.3  . After collision with an electron it is found to have a radius of 21.2 . What is the principal quantum number n of the final state of the atom

(a) n = 4

(b) n = 2

(c) n = 16

(d) n = 3

An AIR station is broadcasting the waves of wavelength 300 metres. If the radiating power of the transmitter is 10 kW, then the number of photons radiated per second is

(a) 1.5

(b) 1.5

(c) 1.5

(d) 1.5

To increase both the resolving power and magnifying power of a telescope:

Material A has critical angle   and material B has critical angle . Then which of the following is true

(i) Light can be totally internally reflected when it passes from B to A

(ii) Light can be totally internally reflected when it passes from A to B

(iii) Critical angle for total internal reflection is  

(iv) Critical angle between A and B is

(a) (i) and (iii)

(b) (i) and (iv)

(c) (ii) and (iii)

(d) (ii) and (iv)