Moving Charges and Magnetism

A closed loop PQRS carrying a current is placed in a uniform magnetic field. If the magnetic forces on segments PS, SR and RQ are F1, F2 and F3 respectively and are in the plane of the paper and along the directions shown, the force on the segment QP is [figure]

1. (F3 - F1)2 - F22
2. F3 - F1 + F2
3. F3 - F1 - F2
4. (F3 - F1)2 + F22

A galvanometer of resistance 50 is connected to a battery of 3 V along with a resistance of 2950 in series. A full scale deflection of 30 divisions is obtained in the galvanometer. In order to reduce this deflection to 20 divisions, the resistance in series should be

1. 6050
2. 4450
3. 5050
4. 5550

Under the influence of a uniform magnetic field, a charged particle moves with constant speed v in a circle of radius R. The time period of rotation of the particle

1. depends on R and not on v
2. is independent of both v and R
3. depends on both v and R
4. depends on v and not on R

The resistance of an ammeter is 13 and its scale is graduated for a current upto 100 amps. After an additional shunt has been connected to this ammeter it becomes possible to measure currents upto 750 amperes by this meter. The value of shunt-resistance is

1. 2
2. 0.2
3. 2 k
4. 20

A charged particle (charge q) is moving in a circle of radius R with uniform speed v. The associated magnetic moment is given by

1. qvR2
2. qvR2/2
3. qvR
4. qvR/2

A beam of electron passes undeflected through mutually perpendicular electric and magnetic fields. If the electric field is switched off, and the same magnetic field is maintained, the electrons move

1. in a circular orbit
2. along a parabolic path
3. along a straight line
4. in an elliptical orbit

In a mass spectrometer used for measuring the masses of ions, the ions are initially accelerated by an electric potential V and then made to describe semicircular paths of radius R using a magnetic field B. If V and B are kept constant, the ratio ( charge on the ionmass of the ion ) will be proportional to

1. 1/R2
2. R2
3. R
4. 1/R

When a charged particle moving with velocity v is subjected to a magnetic field of induction B, the force on it is non-zero. This implies that

1. angle between v and B is either zero or 180
2. angle between v and B is necessarily 90
3. angle between v and B can have any value other than 90
4. angle between v and B can have any value other than zero and 180

Two circular coils 1 and 2 are made from the same wire but the radius of the 1st coil is twice that of the 2nd coil. What ratio of potential difference in volts should be applied across them so that the magnetic field at their centres is the same?

1. 2
2. 3
3. 4
4. 6

A very long straight wire carries a current I. At the instant when a charge +Q at point P has velocity v, as shown, the force on the charge is [figure]

1. along Oy
2. opposite to Oy
3. along Ox
4. opposite to Ox