Electric Charges and Fields — Physics STD 12 Science — Question

When an impurity is doped into an intrinsic semiconductor, the conductivity of the semiconductor:

1. Increases.
2. Decreases.
3. Remains the same.
4. Becomes zero.

X-rays are :

Retina of eye acts like ........ of camera

(a) Shutter

(b) Film

(c) Lens

(d) None of these

If an electric current is passed through a nerve of a man, then man         

(a) Begins to laugh	(b) Begins to weep
(c) Is excited	(d) Becomes insensitive to pain

An electron (charge = 1.6 × 10^–19 coulomb) is moving in a circle of radius 5.1 × 10^–11m at a frequency of 6.8 × 10¹⁵ revolutions/sec.  The equivalent current is approximately

(a) 5.1   amp

(b) 6.8  amp

(c) 1.1  amp

(d) 2.2  amp

The period of the wave will be.

The composition of an a -particle  can be expressed as

(a) 1 P + 1 N

(b) 1 P + 2 N

(c) 2 P + 1 N

(d) 2 P + 2 N

A point source of light is used in a photoelectric effect. If the source is removed farther from the emitting metal, the stopping potential:

A charge q  is placed at the centre of the open end of cylindrical vessel. The flux of the electric field through the surface of the vessel is

(a) Zero

(b)

(c)

(d)