Two similar coils of radius \(R\) are lying concentrically with their planes at right angles to each other. The currents flowing in them are \(I\) and \(2I,\) respectively. What will be the resultant magnetic field induction at the centre?

1.	\(\sqrt{5} \mu_0I \over 2R\)	2.	\({3} \mu_0I \over 2R\)
3.	\( \mu_0I \over 2R\)	4.	\( \mu_0I \over R\)

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 \(F_1, F_2~\text{and}~F_3\) respectively, and are in the plane of the paper and along the directions shown, then which of the following forces acts on the segment \(QP?\)
        

1. \(F_{3} - F_{1} - F_{2}\)

2. \(\sqrt{\left(F_{3} - F_{1}\right)^{2} + F_{2}^{2}}\)

3. \(\sqrt{\left(F_{3} - F_{1}\right)^{2} - F_{2}^{2}}\)

4. \(F_{3} - F_{1} + F_{2}\)

A particle of mass \(m,\) charge \(Q,\) and kinetic energy \(T\) enters a transverse uniform magnetic field of induction \(\vec B.\) What will be the kinetic energy of the particle after seconds?

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 semi-circular paths of radius \(R\) using a magnetic field \(B\). If \(V\) and \(B\) are kept constant, the ratio of \(\left(\frac{\text{Charge on the ion}}{\text{Mass of the ion}} \right)\) will be proportional to:
1. \(\frac{1}{R}\)
2. \(\frac{1}{R^2}\)
3. \(R^2\)
4. \(R\)

A beam of electrons passes un-deflected through mutually perpendicular electric and magnetic fields. Where do the electrons move if the electric field is switched off and the same magnetic field is maintained?