A 250 turn rectangular coil of length 2.1 cm and width 1.25 cm carries a current of      85 $\mu A$ and subjected to the magnetic field of strength 0.85 T. Work done in rotating the coil by 180° against the torque is:

1. $4.55 \mu J$

2. $2.3 \mu J$

3. $1.15 \mu J$

4. $9.5 \mu J$

A thin diamagnetic rod is placed vertically between the poles of an electromagnet. When the current in the electromagnet is switched on, then the diamagnetic rod is pushed up, out of the horizontal magnetic field. Hence the rod gains gravitational potential energy. The work required to do this comes from

1. the current source

2. the magnetic field

3. the lattice structure of the material of the rod

4. the induced electric field due to the changing magnetic field.

The relations amongst the three elements of Earth's magnetic field, namely horizontal component H, vertical component V and  dip angle $\delta$ are, ($B_E$=total magnetic field)

(1) V=$B_E$ tan $\delta$, H=$B_E$

(2) V=$B_E$ sin$\delta$, H=$B_E$ cos$\delta$

(3) V=$B_E$ cos $\delta$, H=$B_E$ sin $\delta$

(4) V=$B_E$, H=$B_E$ tan$\delta$ 

Electromagnets are made of soft iron because soft iron has

1. low retentivity and high coercive force

2. high retentivity and high coercive force

3. low retentivity and low coercive force

4. high retentivity and low coercive force

A compass needle which is allowed to move in a horizontal plane is taken to a geomagnetic pole. It

1. will become rigid showing no movement

2. will stay in any position

3. will stay in north-south direction only

4. will stay in east-west direction only

At a point A on the earth's surface the angle of dip, $\delta =+25°$. At a point B on the earth's surface the angle of dip, $\delta =-25°$. We can interpret that:

1. A and B are both located in the southern hemisphere.

2. A and B are both located in the northern hemisphere.

3. A is located in the southern hemisphere and B is located in the northern hemisphere.

4. A is located in the northern hemisphere and B is located in the southern hemisphere.