Moving Charges and Magnetism

A rigid wire consists of a semicircular portion of radius R and two straight sections. The wire is partially immersed in a perpendicular magnetic field B=B0 k as shown in figure. The magnetic force on the wire if it has a current i is: [figure]

1. iBR j
2. -2iBR j
3. 2iBR j
4. -iBR j

An electron moves through a uniform magnetic field B=B0 i+2B0 j T. At a particular instant of time, the velocity of electron is u=3 i+5 j m/s. If the magnetic force acting on electron is F=5e k N, where e is the charge of electron, then the value of B0 is T.

A uniform magnetic field of 2 10-3 T acts along positive Y-direction. A rectangular loop of sides 20 cm and 10 cm with current of 5 A is in Y-Z plane. The current is in anticlockwise sense with reference to negative X axis. Magnitude and direction of the torque is:

1. 2 10-4 N-m along negative Z-direction
2. 2 10-4 N-m along positive X-direction
3. 2 10-4 N-m along positive Y-direction
4. 2 10-4 N-m along positive Z-direction

Two circular coils P and Q of 100 turns each have same radius of cm. The currents in P and Q are 1 A and 2 A respectively. P and Q are placed with their planes mutually perpendicular with their centers coincide. The resultant magnetic field induction at the center of the coils is x mT, where x= . [Use 0=4 10-7 TmA-1]

Two insulated circular loops A and B of radius 'a' carrying a current of 'I' in the anti clockwise direction as shown in the figure. The magnitude of the magnetic induction at the centre will be : [figure]

1. 2 0 Ia
2. 0 I 2a
3. 0I2a
4. 2 0 Ia

The horizontal component of earth's magnetic field at a place is 3.5 10-5 T. A very long straight conductor carrying current of 2 A in the direction from South east to North West is placed. The force per unit length experienced by the conductor is 10-6 N/m.

A current of 5 A flows in a square loop of side 1 m placed in air. The magnetic field at the centre of the loop is X 2 10-7 T. The value of X is .

The deflection in moving coil galvanometer falls from 25 divisions to 5 divisions when a shunt of 24 is applied. The resistance of galvanometer coil will be :

1. 48
2. 100
3. 96
4. 12

A galvanometer having coil resistance 10 shows a full scale deflection for a current of 3 mA. For it to measure a current of 8 A, the value of the shunt should be:

1. 3.75 10-3
2. 3 10-3
3. 4.85 10-3
4. 2.75 10-3

Two particles X and Y having equal charges are being accelerated through the same potential difference. Thereafter they enter normally in a region of uniform magnetic field and describe circular paths of radii R1 and R2 respectively. The mass ratio of X and Y is :

1. ( R1R2 )
2. ( R2R1 )
3. ( R2R1 )2
4. ( R1R2 )2