Eddy currents are used in:
1. Induction furnace
2. Electromagnetic brakes
3. Speedometers
4. All of these
A short magnet is allowed to fall along the axis of a horizontal metallic ring. Starting from rest, the distance fallen by the magnet in one second may be:
1. \(4\) m
2. \(5\) m
3. \(6\) m
4. \(7\) m
The magnetic flux linked with a coil varies with time as \(\phi = 2t^2-6t+5,\) where \(\phi \) is in Weber and \(t\) is in seconds. The induced current is zero at:
1. \(t=0\)
2. \(t= 1.5~\text{s}\)
3. \(t=3~\text{s}\)
4. \(t=5~\text{s}\)
The net magnetic flux through any closed surface, kept in uniform magnetic field is:
1. zero
2. \(\frac{\mu_{0}}{4 \pi}\)
3. \(4\pi μ_{0}\)
4. \(\frac{4\mu_{0}}{\pi}\)
If a current is passed through a circular loop of radius \(R\) then magnetic flux through a coplanar square loop of side \(l\) as shown in the figure \((l<<R)\) is:
1. \(\frac{\mu_{0} l}{2} \frac{R^{2}}{l}\)
2. \(\frac{\mu_{0} I l^{2}}{2 R}\)
3. \(\frac{\mu_{0} l \pi R^{2}}{2 l}\)
4. \(\frac{\mu_{0} \pi R^{2} I}{l}\)
The radius of a loop as shown in the figure is \(10~\text{cm}.\) If the magnetic field is uniform and has a value \(10^{-2}~ \text{T},\) then the flux through the loop will be:
1. | \(2 \pi \times 10^{-2}~\text{Wb}\) | 2. | \(3 \pi \times 10^{-4}~\text{Wb}\) |
3. | \(5 \pi \times 10^{-5}~\text{Wb}\) | 4. | \(5 \pi \times 10^{-4}~\text{Wb}\) |
Given below are two statements: one is labelled as Assertion (A) and the other is labelled as Reason (R):
Assertion (A): | Self-inductance is called the inertia of electricity. |
Reason (R): | It is on account of self-inductance that the coil opposes any change in current passing through it. |
1. | Both (A) and (R) are true and (R) is the correct explanation of (A). |
2. | Both (A) and (R) are true but (R) is not the correct explanation of (A). |
3. | (A) is true but (R) is false. |
4. | Both (A) and (R) are false. |
Given below are two statements:
Assertion (A): | When a piece of non-metal and a metal are dropped from the same height near the surface of the earth, the non-metallic piece will reach the ground first. |
Reason (R): | Induced current in metal will decrease the acceleration. |
1. | Both (A) and (R) are True and (R) is the correct explanation of (A). |
2. | Both (A) and (R) are True but (R) is not the correct explanation of (A). |
3. | (A) is True but (R) is False. |
4. | Both (A) and (R) are False. |
The current through a choke coil increases from zero to 6 A in 0.3 seconds and an induced emf of 30 V is produced. The inductance of the coil is:
1. | 5 H | 2. | 2.5 H |
3. | 1.5 H | 4. | 2 H |