An aluminum ring B faces an electromagnet A. The current I through A can be altered. Then :

1. Whether I increases or decreases, B will not experience any force

2. If I decrease, A will repel B

3. If I increases, A will attract B

4. If I increases, A will repel B

Two rails of a railway track insulated from each other and the ground are connected to a milli voltmeter. What is the reading of voltmeter, when a train travels with a speed of $180$ km/hr along the track.
(Given that the vertical component of earth's magnetic field is $0.2\times 10^{-4}$ weber/m² and the rails are separated by $1$ m) 
1. $10^{-2}$ V
2. $10^{-4}$ V
3. $10^{-3}$ V
4. $1$ V

A conducting square loop of side $L$ and resistance $R$ moves in its plane with a uniform velocity $v$ perpendicular to one of its sides. A magnetic induction $B$ constant in time and space, pointing perpendicular and into the plane of the loop exists everywhere. The current induced in the loop is:

The magnitude of the earth’s magnetic field at a place is B₀ and the angle of dip is δ. A horizontal conductor of length l lying along the magnetic north-south moves eastwards with a velocity v. The emf induced across the conductor is 

1. Zero

2. B₀lv sinδ

3. B₀lv

4. B₀lv cosδ

A coil and a bulb are connected in series with a DC source, and a soft iron core is then inserted in the coil. Then 

In an LR-circuit, the time constant is that time in which current grows from zero to the value (where I₀ is the steady-state current) 

1. 0.63 I₀

2. 0.50 I₀

3. 0.37 I₀

4. I₀

A copper rod of length l is rotated about one end perpendicular to the magnetic field B with constant angular velocity ω. The induced e.m.f. between the two ends is 

1. $\frac{1}{2}B\omega l^2$

2. $\frac{3}{4}B\omega l^2$

3. $B\omega l^2$

4. $2B\omega l^2$

A circular loop of radius R carrying current I lies in the x-y plane with its centre at the origin. The total magnetic flux through the x-y plane is 

1. Directly proportional to I

2. Directly proportional to R

3. Directly proportional to R²

4. Zero