A small circular flexible loop of wire of radius 'r' carries a current I. It is placed in a uniform magnetic field B. The tension in the loop will be doubled if :

• I is doubled

• B is halved

• r is doubled

• Both B and I are doubled

Two parallel wires carrying current in the same direction attract each other because of :

• the potential difference between them

• mutual inductance between them

• the electric force between them

• the magnetic force between them

A galvanometer has a resistance of 400 Ω and deflects full scale for a current of 0.2 mA through it. The shunt resistance required to covert it into 3A ammeter is :

• 0.027 Ω

• 0.054 Ω

• 0.0135 Ω

• none of these

A coil having N turns carries a current as shown in the figure. The magnetic field intensity at point P is :

• $\frac{{\mathrm{\mu }}_0{\mathrm{NiR}}^2}{2({\mathrm{R}}^2 + {\mathrm{x}}^2{)}^{3/2}}$

• $\frac{{\mathrm{\mu }}_0\mathrm{Ni}}{2\mathrm{R}}$

• $\frac{{\mathrm{\mu }}_0{\mathrm{NiR}}^2}{(\mathrm{R} + \mathrm{x}{)}^2}$

• zero

An electron moves at a right angle to a magnetic field of 1.5 x 10^-2 tesla with a speed of 6 x 10⁷ m/s. If the specific charge of the electron is 1.7 x 10¹¹ coulomb/kg, the radius of the circular path will be

• 2.9 cm

• 3.9 cm

• 2.35 cm

• 2 cm

A charged particle is moving in a uniform magnetic field in a circular path of radius R. When energy of the particle is doubled, then the new radius will be:

• R

• R$\sqrt{2}$

• R/$\sqrt{2}$

•  2R

297.

Magnetic and electric field are acting on a proton moving with velocity $\mathrm{\nu }$. Proton will be undeflected if 

• E is parallel to v, but perpendicular to B

• E and B both are parallel to v

• E and B are perpendicular to each other

• E, B and v are perpendicular to one another and v=$\frac{\mathrm{E}}{\mathrm{B}}$

A current of 0.1 ampere is flowing through a coil of 1000 turns and radius 0.1 metre. The magnetic field at the centre of the coil is

• 2 × 10⁻¹ T

• 4.31 × 10⁻²  T

• 6.28 × 10⁻⁴  T

• 9.81 × 10⁻⁴  T

In a galvanometer of 5 ohm resistance, a wire of 2 ohm resistance is used as a shunt. If the total current is 1 ampere, the fraction of current that will flow through the shunt is

• 1.2 A

• 0.7 A

• 0.5 A

• 0.3 A

A solenoid of length 5O cm and a radius of cross-section 1 cm has 1000 turns of wire wound over it. If the current carried is 5 A, the magnetic field on its axis, near the centre of the solenoid is approximately (permeability of free space ${\mathrm{\mu }}_0$= $4\mathrm{\pi } \times {10}^{-7}$ T-m/A)

• 0.63 × 10⁻² T

• 1.26 × 10⁻² T

• 2.51 × 10⁻² T

• 6.3 T