31.

Two charges each of equal magnitude 3.2 x 10^-19 coulomb but of opposite sign form an electric dipole. The distance between the two charges is 2.4 $\stackrel{\circ }{\mathrm{A}}$. If the dipole is placed in an electric field of 5 x 10⁵ volt/metre, then in equilibrium its potential energy will be

• 3 × 15^-23 joule

• -3.84 × 10^-23 joule

• -6 × 10^-23 joule 

• -2 × 10^-26 joule 

A resistance of 8 ohm and an inductance of 6 ohm are connected in series to an A.C circuit. The impedence of the circuit is

• 14$\sqrt{2} \mathrm{\Omega }$

• 10 $\mathrm{\Omega }$

• 2$\mathrm{\Omega }$

• 15 $\mathrm{\Omega }$

Lenz's law is based on the principle of conservation of

• mass

• charge

• momentum

• energy

A battery of 12 volt is charged by a supply of 100 volt as shown in the figure. The charging current is 1.0A. Calculate the value of R

• 45 $\mathrm{\Omega }$

• 105 $\mathrm{\Omega }$

• 88 $\mathrm{\Omega }$

• 95 $\mathrm{\Omega }$

At an instant a positive charge is moving parallel to a current carrying conductor. The path of the positive charge is

• elliptical

• circle

• straight line

• parabola

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

At a certain place, magnitude of horizontal and vertical components of a magnetic field are same. The total intensity of magnetic field at that place will be

• H

• H²

• 2H

• $\sqrt{2 } \mathrm{H}$

A coil having resistance of 50 ohm and an inductance of 10 ohm, is connected to a 100 volt battery. The energy stored in the coil is

• 10 J

• 20 J

• 30 J

• 40 J

A capacitor when charged by a potential difference of 200 volt, stores a charge of 0.1 C. By discharging, energy liberated by the capacitor is

• -30 J

• -15 J

• 10 J

• 20 J

A small current carrying loop acts as a small magnet. The area of the loop is A and magnetic moment is M. The current in the loop will be

• $\frac{\mathrm{A}}{\mathrm{M}}$

• $\frac{\mathrm{M}}{\mathrm{A}}$

• MA

• A²M