Self-inductances of primary and secondary of an ideal transformer are 90 mH and 40 mH. If the current in the primary decreases at the rate 103 As-1, then emf across the secondary is
1. 40 V
2. 90 V
3. 60 V
4. 20 V
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 |
In the figure as shown, straight wire carries a constant current. The direction of induced current in the rotating loop about an axis xx' at the instant shown
1. is anticlockwise.
2. is clockwise.
3. there is no current in the loop.
4. maybe clockwise or anticlockwise.
The figure shows a circular region of radius R in which uniform magnetic field is increasing at a constant rate dB/dt = . The induced electric field at a distance r from the centre is
1. for all values of r
2. for all values of r
3. for rR and for rR
4. for rR and for rR
If the instantaneous charge in the capacitor is 400C and current through the circuit is decreasing at the rate 103 A/s, then potential difference VA-VB is equal to
1. 30 V
2. Zero
3. 10 V
4. 70 V
A uniform rod rotates in a uniform magnetic field B (perpendicular to its length) about its one of the end with constant angular velocity. The electric field produced is
1. Uniform along its length
2. Non-uniform along its length
3. May be uniform or non-uniform
4. Cannot be predicted
When the current in a coil changes from 0 to 5 A, in 0.5 s, the average induced emf in the coil is 1 volt. The self-inductance of the coil is
1. 0.1H
2. 0.2H
3. 0.4H
4. 1.5H
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. | \(t=5~\text{s}\) |
Choke coil works on the principle of
1. Kirchhoff's law
2. Self-induction
3. Mutual induction
4. All of these
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. |