An electron moving in a circular orbit of radius r makes n rotations per second. The magnetic field produced at the centre has magnitude:

$1. \frac{{\mu }_{0}ne}{2\pi r}$
$2. Zero$
$3. \frac{n^{2}e}{r}$
$4. \frac{{\mu }_{0}ne}{2r}$

A proton and an alpha particle both enter a region of uniform magnetic field B, moving at right angles to the field B. If the radius of circular orbits for both the particles is equal and the kinetic energy acquired by proton is 1 MeV, the energy acquired by the alpha particle will be

(1)4 MeV

(2) 0.5 MeV

(3) 1.5 MeV

(4) 1 MeV

Two identical long conducting wires AOB and COD are placed at right angle to each other, with one above other such that O is their common point for the two. The wires carry  I₁ and I₂ currents, respectively. Point P is lying at distance d from 0 along a direction perpendicular to the plane containing the wires. The magnetic field at the point P will be

(1) μ_o/2πd(I₁/I₂)

(2)μ_o/2πd (I₁+I₂)

(3)μ_o/2πd(I₁²-I₂²)

(4)μ_o/2πd(I₁²+I₂²)^1/2

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. $-\sqrt{2}\mathbf{F}$