Magnetism And Matter — Physics STD 12 Science — Question

The work functions of metals A and B are in the ratio 1 : 2. If light of frequencies f  and 2f are incident on the surfaces of A and B respectively, the ratio of the maximum kinetic energies of photoelectrons emitted is (f is greater than threshold frequency of A, 2f is greater than threshold frequency of B)

(a) 1 : 1

(b) 1 : 2

(c) 1 : 3

(d) 1 : 4

Which of the following reaction must be initiated by the neutron?

When NPN transistor is used as an amplifier

(a) Electrons move from base to emitter

(b) Electrons move from emitter to base

(c) Electrons moves from base to emitter

(d) Holes moves from base to emitter

The number of photo electrons emitted for light of a frequency v (higher than the threshold frequency v₀​) is proportional to:

Name the unit in which work function of a metal is generally expressed.

A short magnet of moment 6.75 Am² produces a neutral point on its axis. If horizontal component of earth's magnetic field is 5  , then the distance of the neutral point should be

(a) 10 cm

(b) 20 cm

(c) 30 cm

(d) 40 cm

Electric lines of force:

Assertion :   Through the same current flows through the line wires and the filament of the bulb but heat produced in the filament is much higher then that in line wires.

Reason     : The filament of bulbs is made of a material of high resistance and high melting point.

(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.

Two electric charges 12μC and -6 μC  are placed 20 cm apart in air. There will be a point P on the line joining these charges and outside the region between them, at which the electric potential is zero. The distance of P from -6 μC  charge is

(a) 0.10 m

(b) 0.15 m

(c) 0.20 m

(d) 0.25 m