Current Electricity — Physics STD 12 Science — Question

When a charged particle enters a uniform magnetic field its kinetic energy

(a) Remains constant

(b) Increases

(c) Decreases

(d) Becomes zero

A short-circuited coil is placed in a time-varying magnetic field. Electrical power is dissipated due to the current induced in the coil. If the number of turns were to be quadrupled and the wire radius halved, the electrical power dissipated would be

(a) Halved

(b) The same

(c) Doubled

(d) Quadrupled

The direction of line of magnetic field of bar magnet is

(a) From south pole to north pole

(b) From north pole to south pole

(c) Across the bar magnet

(d) From south pole to north pole inside the magnet and from north pole to south pole outside the magnet

When electron beam passes through an electric field, they gain kinetic energy. If the same beam passes through magnetic field, then

(a) Their energy increases

(b) Their momentum increases

(c) Their potential energy increases

(d) Energy and momentum both remains unchanged

Boron rods in a nuclear reactor are used to:

A copper rod of length l is rotated about one end perpendicular to the magnetic field B with constant angular velocity ω. The induced e.m.f. between the two ends is

(a)

(b)

(c)

(d)

In an area of constant magnetic field, a charged particle enters in a direction parallel to the direction of magnetic field with its velocity. The speed of particle is:

An N-type semiconductor is:

A double convex lens of glass of m = 1.5 has radius of curvature of each of its surface is 0.2 m.  The power of the lens is

(a) + 10 dioptres

(b) – 10 dioptres

(c) – 5 dioptres

(d)  +5 dioptres

There are three voltmeters of the same range but of resistances 1000Ω, 8000 Ω and 4000 Ω  respectively.  The best voltmeter among these is the one whose resistance is

(a) 10000 W

(b) 8000 W

(c) 4000 W

(d) All are equally good