Moving Charges and Magnetism

The electrostatic force ( F1 ) and magnetic force ( F2 ) acting on a charge q moving with velocity v can be written :

1. F1 = q B, F2 = q( B v)
2. F1 = q V E, F2 = q( B V)
3. F1 = q E, F2 = q( V B)
4. F1 = q E, F2 = q( B V)

A solenoid of length 0.5 m has a radius of 1 cm and is made up of 'm' number of turns. It carries a current of 5 A. If the magnitude of the magnetic field inside the solenoid is 6.28 10-3 T then the value of m is .

An electron is projected with uniform velocity along the axis inside a current carrying long solenoid. Then :

1. the electron will experience a force at 45 to the axis and execute a helical path.
2. the electron will be accelerated along the axis.
3. the electron path will be circular about the axis.
4. the electron will continue to move with uniform velocity along the axis of the solenoid.

The magnetic field existing in a region is given by B=0.2(1+2x) k. A square loop of edge 50 cm carrying 0.5 A current is placed in x-y plane with its edges parallel to the x-y axes, as shown in figure. The magnitude of the net magnetic force experienced by the loop is mN. [figure]

Two parallel long current carrying wires separated by a distance 2r are shown in the figure. The ratio of magnetic field at A to the magnetic field produced at C is x7. The value of x is . [figure]

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