Electric Charges and Fields — Physics STD 12 Science — Question

Induction occurs due to ______?

Two spheres A and B of exactly same mass are given equal positive and negative charges respectively. Their masses after charging.

If the forward voltage in a semiconductor diode is doubled, the width of the depletion layer will

(a) Become half

(b) Become one-fourth

(c) Remain unchanged

(d) Become double

An electron of mass  initially at rest moves through a certain distance in a uniform electric field in time . A proton of mass  also initially at rest takes time  to move through an equal distance in this uniform electric field. Neglecting the effect of gravity, the ratio of  is nearly equal to

(a) 1

(b)

(c)

(d) 1836

Five balls numbered 1 to 5 are suspended using separate threads. Pairs (1, 2), (2, 4) and (4, 1) show electrostatic attraction, while pair (2, 3) and (4, 5) show repulsion. Therefore ball 1 must be

(a) Positively charged

(b) Negatively charged

(c) Neutral

(d) Made of metal

Which of the following is not an application of eddy currents

(a) Induction furnace	(b) Galvanometer damping
(c) Speedometer of automobiles	(d) X-ray crystallography

A 25 watt, 220 volt bulb and a 100 watt, 220 volt bulb are connected in parallel across a 220 volt line. Which bulb will glow more brightly

(a) 25 watt bulb	(b) 100 watt bulb
(c) Both will have same brightness	(d) First 25 watt then 100 watt

Two thick wires and two thin wires, all of the same materials and same length form a square in the three different ways P, Q and R as shown in fig with current connection shown, the magnetic field at the centre of the square is zero in cases

(a) In P only

(b) In P and Q only

(c) In Q and R only

(d)  P and R only

If ‘p’ region of a semi conductor is connected to negative and ‘n’ region to positive pole, it is said to be:

A long thin hollow metallic cylinder of radius 'R' has a current i ampere. The magnetic induction 'B'-away from the axis at a distance r from the axis varies as shown in

(a)

(b)

(c)

(d)