A thin semicircular conducting ring (PQR) of radius r is falling with its plane vertical in a horizontal magnetic field B, as shown in figure. The potential difference developed across the ring when its speed is v, is


(1) zero

(2) Bvπr²/2 and P is at higher potential

(3) πrBv and R is at higher potential  

(4) 2rBv and R is at higher potential

When a proton is released from rest in a room, it starts with an initial acceleration $a_o$ towards west. When it is projected towards north with a speed $v_o$ , it moves with an initial acceleration 3$a_o$ towards west. The electric and magnetic fields in the room are 

(1) ma_o/e west, 4ma_o/ev_o up

(2) ma_o/e west, 2ma_o/ev_o down

(3) ma_o/e east, 3ma_o/ev_o up

(4) ma_o/e east, 3ma_o/ev_o down

A current loop in a magnetic field

(1) experiences a torque whether the field is uniform or non-uniform in all orientations

(2) can be in equilibrium in one orentations.

(3) can be equilibrium in two orientations, both the wquilibriu states are unstable

(4) can be in equilibrium in two orientations, one stable while the other is unstable

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. The resultant magnetic field induction at the centre will be 

(1)$\frac{\sqrt{5}{\mu }_{0}I}{2R}$                                         

(2)$\frac{3{\mu }_{0}I}{2R}$

(3)$\frac{{\mu }_{0}I}{2R}$                                             

(4)$\frac{{\mu }_{0}I}{R}$

An alternating electric field of frequency \(\nu\), is applied across the dees (radius=R) of a cyclotron that is being used to accelerate protons(mass=m). The operating magnetic field (B) used in the cyclotron and the kinetic energy (K) of the proton beam, produced by it, are given by:

1. \(\mathrm{B}=\frac{m \nu}{\mathrm{e}}\) and \(K=2 m \pi^{2} \mathrm{\nu}^{2} \mathrm{R}^{2}\) $\frac{}{}\mathrm{}{\mathrm{}}^{\mathrm{}}{\mathrm{}}^{\mathrm{}}{\mathrm{}}^{\mathrm{}}$

2.$\frac{\mathrm{}\mathrm{}}{}{}^{\mathrm{}}{}^{\mathrm{}}$\(\mathrm{B}=\frac{2\pi m \nu}{\mathrm{e}}\) and \(K=m^2 \pi \mathrm{\nu} \mathrm{R}^{2}\)

3. ${\mathrm{}}^{\mathrm{}}$\(\mathrm{B}=\frac{2\pi m \nu}{\mathrm{e}}\) and \(K=2 m \pi^{2} \mathrm{\nu}^{2} \mathrm{R}^{2}\)

4. ${}^{\mathrm{}}$\(\mathrm{B}=\frac{m \nu}{\mathrm{e}}\) and \(K=m^2 \pi \mathrm{\nu} \mathrm{R}^{2}\)

A proton carrying 1 MeV kinetic energy is moving in a circular path of radius R in a uniform magnetic field. What should be the energy of an $\mathrm{\alpha }$-particle to describe a circle of the same radius in the same field?

1. 2 MeV                  2. 1 MeV

3. 0.5 MeV               4. 4 MeV

A current-carrying closed loop in the form of a right-angle isosceles triangle ABC is placed in a uniform magnetic field acting along AB. If the magnetic force on the arm BC is F, the force on the arm AC is:

1. $\mathbf{-}\mathbf{F}$                                               2. $\mathbf{F}$

3. $\sqrt{2}\mathbf{F}$                                             4. $-\sqrt{2}\mathbf{F}$

A uniform electric field and a uniform magnetic field are acting in the same direction in a certain region. If an electron is projected in the region such that its velocity is pointed along the direction of fields, then the electron :

1. speed will decrease

2. speed will increase 

3. will turn towards the left of the direction of motion 

4. will turn towards right of direction a motion

A galvanometer of resistance, G is shunted by a resistance S ohm. To keep the main current in the circuit unchanged, the resistance to be put in series with the galvanometer is

(1) $\frac{S^{\mathit{2}}}{(S+G)}$                                             

(2) $\frac{SG}{(S+G)}$

(3) $\frac{G^{\mathit{2}}}{(S+G)}$                                             

(4) $\frac{G}{(S+G)}$

A square loop, carrying a steady current I, is placed in a horizontal plane near a long straight conductor carrying a steady current $I_{\mathit{1}}$ at a distance d from the conductor as shown in figure. The loop will experience 

(1) a net repulsive force away from the conductor 

(2) a net torque acting upward perpendicular to the horizontal plane

(3) a net torque acting downward normal to the horizontal plane

(4) a net attractive force towards the conductor