## 71. Three point charges q, q and -2q are located at (0, -a, a), (0, a, a) and (0, 0, -a), respectively. The net dipole moment of this charge distribution is

## 72. Consider the following three independent cases:

i. Particle A of charge +q moves in free space with a constant velocity $$\overrightarrow {\bf{v}} $$ (v ≪ speed of light).

ii. Particle B of charge +q moves in free space in a circle of radius R with same speed v as In case i.

iii. Particle C having charge -q moves as in case ii.

If the powers radiated by A, B and C are P_{A}, P_{B} and P_{C} respectively then

i. Particle A of charge +q moves in free space with a constant velocity $$\overrightarrow {\bf{v}} $$ (v ≪ speed of light).

ii. Particle B of charge +q moves in free space in a circle of radius R with same speed v as In case i.

iii. Particle C having charge -q moves as in case ii.

If the powers radiated by A, B and C are P

_{A}, P

_{B}and P

_{C}respectively then

## 73. An infinitely long wire carrying a current $$I\left( t \right) = {I_0}\cos \left( {\omega t} \right)$$ is placed at a distance a from a square loop of side a as shown in the figure. If the resistance of the loop is R, then the amplitude of the induced current in the loop is

## 74. A large circular coil of N turns and radius R carries a time varying current $$I = {I_0}\sin \left( {\omega t} \right).$$ A small circular coil of n turns and radius r(r ≪ R) is placed at the centre of the large coil such that the coils are concentric and coplanar. The induced emf in the small coil

## 75. A conducting loop L of surface area S is moving with a velocity $$\overrightarrow {\bf{v}} $$ in a magnetic field $$\overrightarrow {\bf{B}} \left( {\overrightarrow {\bf{r}} ,\,t} \right) = {B_0}{t^2},\,{B_0}$$ is a positive constant of suitable dimensions. The emf
induced V_{emf} in the loop is given by

_{emf}in the loop is given by

## 76. Unpolarized light falls from air to a planar air-glass interface (refractive index of glass is 1.5) and the reflected light is observed to be plane polarized. The polarization vector and the angle of incidence θ_{i} are

_{i}are

## 77. Consider the given statements about E(r, t) and B(r, t), the electric and magnetic vectors respectively in a region of free space

P. Both E and B are conservative vector fields.

Q. Both E and B are central force fields.

R. E and B are mutually perpendicular in the region.

S. Work done by B on a moving charge in the region is zero.

Choose the right combination of correct statements from the following.

P. Both E and B are conservative vector fields.

Q. Both E and B are central force fields.

R. E and B are mutually perpendicular in the region.

S. Work done by B on a moving charge in the region is zero.

Choose the right combination of correct statements from the following.