## Monday, May 12, 2008

### Past JEE Objective Questions - Magnetism - Part 1

1982

1(viii) A magnetic needle is kept in a non uniform magnetic field. It experiences

a. a force and a torque
b. a force but not a torque
c. a torque but not a force
d. neither a force nor a torque

1983
1(viii) A conducting circular loop of radius r carries a constant current i. It is placed in a uniform magnetic field (vector) B0 such that vector (B0) is perpendicular to the plane of the loop. The magnetic force acting on the loop is

a. irB0
b. 2 πirB0
c. zero
d. 2 πirB0

4(vii) state true or false.

There is no change in the energy of a charged particle moving in a magnetic field although a magnetic force is acting on it.

(viii) State whether the following statement is true or false
A charged particle enters a region of uniform magnetic field at angle of 85° to the magnetic lines of force. The path of the particle is circle.

1984

1(v) A proton with a constant velocity passes through a region of space without ny change in its velocity. If E and B represent the electric and magnetic fields respectively, this region of space may have:

a. E = 0, B = 0
b. E = 0, B ≠0
c. E≠0, B = 0
d. E≠0, B ≠0

3(vii) State whether the following statement is true or false.

An electron and a proton are moving with the same kinetic energy along the same direction. When they pass through a uniform magnetic field perpendicular to the direction of their motion, they describe circular paths of the same radius.

1986
1(vii) Two thin long parallel wires separated by a distance b are carrying a current i each. The magnitude of the force per unit length exerted by one wire on the other is

a. µ0i²/b²
b. µ0i²/2πb
c. µ0i/2πb
d. µ0i/2πb²

3(iv) State whether the following statement is true or false

A coil of metal wire is kept stationary in a non-uniform magnetic field. An emf is induced in the coil.

1987
2(ix) A wire of length L metres carrying a current i amperes is bent in the form of a circle. The magnitude of its magnetic moment is ----------------- in MKS units.

3(iv) State whether the following statement is true or false

A conducting rod AB (parallel to the Y-axis) moves parallel to the x-axis in a uniform magnetic field pointing in the positive z-direction. The end A of the rod gets positively charged.

1988

2(iv) Two particles of X and Y having equal charge, after being accelerated through the same potential difference enter a region of uniform magnetic field and describe circular paths of radii R1 and R2 respectively. The ratio of the mass of X to the mass of Y is

a. (R1/R2 1/2
b. R2/R1
c. (R1/R2)²
d. R1/R2

3(i) In the formual X = 3YZ², X and Z have dimensions of capacitance and magnetic induction respectively. The dimensions of Y in MKSQ system are-------------------

3(viii) The semicircular wireloop PQRSP is formed by joining two semicircular wires of radii R1 and R2. The radius of SP of the loop is R2 and the radius of RQ of the loop is R1 (R1