Moving Charges and Magnetism

A galvanometer has a resistance of 50 and it allows maximum current of 5 mA. It can be converted into voltmeter to measure up to 100 V by connecting in series a resistor of resistance :

1. 19500
2. 5975
3. 20050
4. 19950

A regular polygon of 6 sides is formed by bending a wire of length 4 meter. If an electric current of 4 3 A is flowing through the sides of the polygon, the magnetic field at the centre of the polygon would be x 10-7 T. The value of x is .

In an ammeter, 5\% of the main current passes through the galvanometer. If resistance of the galvanometer is G, the resistance of ammeter will be :

1. G200
2. G199
3. 199 G
4. 200 G

A moving coil galvanometer has 100 turns and each turn has an area of 2.0 cm2. The magnetic field produced by the magnet is 0.01 T and the deflection in the coil is 0.05 radian when a current of 10 mA is passed through it. The torsional constant of the suspension wire is x 10-5 N-m/rad. The value of x is .

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.