Alternating Current — Physics STD 12 Science — Question

Rate of change of torque τ with deflection θ is maximum for a magnet suspended freely in a uniform magnetic field of induction B, when

(a) θ = 0°

(b) θ = 45°

(c) θ = 60°

(d) θ = 90°

Assuming photoemission to take place, the factor by which the maximum velocity of the emitted photoelectrons changes when the wavelength of the incident radiation is increased four times, is

(a) 4

(b)

(c) 2

(d)

Consider a region inside which there are various types of charges but the total charge is zero. At points outside the region:

Photons of energies 1 eV and 2 eV are successively incident on a metallic surface of work function 0.5 eV. The ratio of kinetic energy of most energetic photoelectrons in the two cases will be :

GaAs is

(a) Element semiconductor	(b) Alloy semiconductor
(c) Bad conductor	(d) Metallic semiconductor

Assertion  :   There is no atmosphere on moon

Reason      : Escape velocity at the surface of moon is low.

(a) If both assertion and reason are true and the reason is the correct explanation of the assertion.

(b) If both assertion and reason are true but reason is not the correct explanation of the assertion.

(c) If assertion is true but reason is false.

(d) If the assertion and reason both are false.

If the ratio of intensities of two waves is 1 : 25, then the ratio of their amplitudes will be

(a) 1 : 25

(b) 5 : 1

(c) 26 : 24

(d) 1 : 5

A coil of 100 turns and area 5 square centimetre is placed in a magnetic field B = 0.2 T. The normal to the plane of the coil makes an angle of 60° with the direction of the magnetic field. The magnetic flux linked with the coil is

(a) 5

(b) 5

(c)

(d)

What happens during regulation action of a Zener diode?

Conductivity of semiconductors: