Alternating Current — Physics STD 12 Science — Question

A particle is fastened at the end of a string and is whirled in a vertical circle with the other end of the string being fixed. The motion of the particle is:

1. Periodic.
2. Oscillatory.
3. Simple harmonic.
4. Angular simple harmonic.

In Bohr’s model, if the atomic radius of the first orbit is  , then the radius of the fourth orbit is

(a)

(b) 4

(c)

(d) 16

A sinusoidal voltage of peak value 200 volt is connected to a diode and resistor R in the circuit shown so that half wave rectification occurs. If the forward resistance of the diode is negligible compared to R the rms voltage (in volt) across R is approximately

(a) 200

(b) 100

(c)

(d) 280

A radioactive sample of U²³⁸ decay to Pb through a process for which half life is 4.5 × 10⁹ years. The ratio of number of nuclei of Pb to U²³⁸ after a time  of 1.5 × 10⁹ years (given 2^1/3 = 1.26)

(a) 0.12

(b) 0.26

(c) 1.2

(d) 0.37

Mass number is denoted by:

The drift current in a p-ri junction is:

1. From the n-side to the p-side.
2. From the p-side to the n-side.
3. From the n-side to the p-side if the junction is forward-biased and in the opposite direction if it is reverse-biased.
4. From the p-side to the n-side if the junction is forward-biased and in the opposite direction if it is reverse-biased.

Huygen wave theory allows us to know

(a) The wavelength of the wave	(b) The velocity of the wave
(c) The amplitude of the wave	(d) The propagation of wave fronts

Which theory is confirmed by the Davisson – Germer experiment?

When the  current in a coil changes from 8 ampere to 2 ampere in 3  second, the e.m.f. induced in the coil is 2 volt. The self inductance of the coil (in millihenry) is

(a)  1

(b) 5

(c)  20

(d) 10

When a metal is illuminated with light wave, then the minimum energy required to take an electron just out of the surface of the metal is called :