Electric Charges and Fields — Physics STD 12 Science — Question

A circular current carrying coil has a radius R. The distance from the centre of the coil on the axis where the magnetic induction will be   to its value at the centre of the coil, is

(a)

(b) R

(c) 2

(d)

The maximum electric field that a dielectric medium can withstand without break-down is called its:

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

Half-life of a substance is 10 years. In what time, it becomes  th part of the initial amount

(a) 5 years

(b) 10 years

(c) 20 years

(d) None of these

In a semiconductor, the forbidden energy gap between the valence band and the conduction band is of the order is:

A light of wavelength 5890 Å falls normally on a thin air film. The minimum thickness of the film such that the film appears dark in reflected light

(a) 2.945

(b) 3.945

(c) 4.95

(d) 1.945

Through a semiconductor, an electric current is due to drift of

(a) Free electrons	(b) Free electrons and holes
(c) Positive and negative ions	(d) Protons

A current of 1 mA is flowing through a copper wire.  How many electrons will pass a given point in one second [e = 1.6 × 10^–19 Coulomb]

(a) 6.25 ×

(b) 6.25 ×

(c) 6.25 ×

(d) 6.25 ×

Thirteen resistances each of resistance R ohm are connected in the circuit as shown in the figure below.  The effective resistance between A and B is

(a) 2R W

(b)

(c)

(d) R W