A coil of one loop is made from a wire of length L and thereafter a coil of two loops is made from same wire. The ratio of magnetic field at the centre of the coils will be:
1.  1 : 4
2.  1 : 1
3.  1 : 8
4.  4 : 1

Resistance of a Galvanometer coil is $8~\Omega$ and $2~\Omega$ shunt resistance is connected with it. If main current is $1$ A then the current flow through $2~\Omega$ resistance will be:
1. $0.2$ A
2. $0.8$ A
3. $0.1$ A
4. $0.4$ A

Two long parallel wires are at a distance of $1$ m. If both of them carry one ampere of current in the same direction, then the force of attraction on the unit length of the wires will be:
1. $2\times10^{-7}$ N/m
2. $4\times10^{-7}$ N/m
3. $8\times10^{-7}$ N/m
4. $10^{-7}$ N/m

A current-carrying coil (I = 5A, R = 10 cm) has 50 turns. The magnetic field at its centre will be:
1.  1.57 mT
2.  3.14 mT
3.  1 mT
4.  2 mT

Two identically charged particles A and B initially at rest, are accelerated by a common potential difference V. They enter into a transverse uniform magnetic field B. If they describe a circular path of radii  $r_1$ $and$ $r_2$ respectively, then their mass ratio is:

1.  ${\left(\frac{r_1}{r_2}\right)}^2$

2. ${\left(\frac{r_2}{r_1}\right)}^2$

3. $\left(\frac{r_1}{r_2}\right)$

4. $\left(\frac{r_2}{r_1}\right)$

For the adjoining figure, the magnetic field at a point 'P' will be:

1. $\frac{{\mu }_0}{4\pi }\odot$

2. $\frac{{\mu }_0}{\pi }\otimes$

3. $\frac{{\mu }_0}{2\pi }\otimes$

4. $\frac{{\mu }_0}{2\pi }\odot$

A charge having q/m equal to 10⁸ c/kg and with velocity 3 × 10⁵ m/s enters into a uniform magnetic field B = 0.3 tesla at an angle 30º with the direction of field. Then the radius of curvature will be:

1. 0.01 cm

2. 0.5 cm

3. 1 cm

4. 2 cm

An electron having mass 'm' and kinetic energy E enter in a uniform magnetic field B perpendicularly. Its frequency will be:

1. $\frac{eE}{qVB}$

2. $\frac{2\mathrm{\pi m}}{eB}$

3. $\frac{eB}{2\mathrm{\pi m}}$

4. $\frac{2m}{eBE}$

In the Thomson mass spectrograph where $\vec{E}\perp\vec{B}$ the velocity of the undeflected electron beam will be:
1. $\frac{\left| \vec{E}\right|}{\left|\vec{B} \right|}$
2. $\vec{E}\times \vec{B}$
3. $\frac{\left| \vec{B}\right|}{\left|\vec{E} \right|}$
4. $\frac{E^{2}}{B^{2}}$

The tangent galvanometer is used to measure: 
1.  Potential difference
2.  Current
3.  Resistance
4.  In measuring the charge