Atoms — Physics STD 12 Science — Question

Let n_p and n_e be the number of holes and conduction electrons in an intrinsic semiconductor.

A proton exerts a force on a proton which is:

1. Gravitational.
2. Electromagnetic.
3. Nuclear.
4. Weak.

Water equivalent of a body is measured in:

1. Kg
2. Calorie
3. Kelvin
4. m³

In comparison to a half wave rectifier, the full wave rectifier gives lower

(a) Efficiency	(b) Average dc
(c) Average output voltage	(d) None of these

When hydrogen atom is in its first excited level, its radius is .... its ground state radius

(a) Half

(b) Same

(c) Twice

(d) Four times

The current flowing through a lamp marked as 50 W and 250 V is

(a) 5 amp

(b) 2.5 amp

(c) 2 amp

(d) 0.2 amp

A cable of resistance 10 Ω carries electric power from a generator producing 250 kW at 10000 volt. The current in the cable is

(a) 25 A

(b) 250 A

(c) 100 A

(d) 1000 A

In an apparatus, the electric field was found to oscillate with an amplitude of 18 V/m. The magnitude of the oscillating magnetic field will be

(a) 4  T

(b) 6 T

(c) 9 T

(d) 11  T

A charged particle is whirled in a horizontal circle on a frictionless table by attaching it to a string fixed at one point. If a magnetic field is switched on in the vertical direction the tension in the string.

1. Will increase.
2. Will decrease.
3. Will remain the same.
4. May increase or decrease.

In a cathode ray oscillograph, the focusing of beam on the screen is achieved by: