A coil of self-inductance \(L\) is connected in series with a bulb \(\mathrm{B}\) and an AC source. The brightness of the bulb decreases when:
1. | number of turns in the coil is reduced. |
2. | a capacitance of reactance \(X_C = X_L\) is included in the same circuit. |
3. | an iron rod is inserted in the coil. |
4. | frequency of the AC source is decreased. |
The current (\(I\)) in the inductance is varying with time (\(t\)) according to the plot shown in the figure.
1. | 2. | ||
3. | 4. |
The current \(i\) in a coil varies with time as shown in the figure. The variation of induced emf with time would be:
1. | 2. | ||
3. | 4. |
A conducting circular loop is placed in a uniform magnetic field of 0.04 T with its plane perpendicular to the magnetic field. The radius of the loop starts shrinking at a rate of 2 mm/s. The induced e.m.f. in the loop when the radius is 2 cm is:
1. \(3.2\pi ~\mu V\)
2. \(4.8\pi ~\mu V\)
3. \(0.8\pi ~\mu V\)
4. \(1.6\pi ~\mu V\)
A rectangular, a square, a circular, and an elliptical loop, all in the (x-y) plane, are moving out of a uniform magnetic field with a constant velocity, . The magnetic field is directed along the negative z-axis direction. The induced emf, during the passage of these loops out of the field region, will not remain constant for:
1. | the rectangular, circular, and elliptical loops. |
2. | the circular and the elliptical loops. |
3. | only the elliptical loop. |
4. | any of the four loops. |
The primary and secondary coils of a transformer have \(50\) and \(1500\) turns respectively. If the magnetic flux \(\phi\) linked with the primary coil is given by \(\phi=\phi_0+4t,\) where \(\phi\) is in Weber, \(t\) is time in seconds, and \(\phi_0\) is a constant, the output voltage across the secondary coil is:
1. \(90~\mathrm{V}\)
2. \(120~\mathrm{V}\)
3. \(220~\mathrm{V}\)
4. \(30~\mathrm{V}\)
Two coils of self-inductance 2 mH and 8 mH are placed so close together that the effective flux in one coil is completely linked with the other. The mutual inductance between these coils is:
1. 10 mH
2. 6 mH
3. 4 mH
4. 16 mH
In which of the following devices, the eddy current effect is not used?
1. | electric heater |
2. | induction furnace |
3. | magnetic braking in train |
4. | electromagnet |
A \(800\) turn coil of effective area \(0.05~\text{m}^2\) is kept perpendicular to a magnetic field \(5\times 10^{-5}~\text{T}\). When the plane of the coil is rotated by \(90^{\circ}\)around any of its coplanar axis in \(0.1~\text{s}\), the emf induced in the coil will be:
1. \(0.02~\text{V}\)
2. \(2~\text{V}\)
3. \(0.2~\text{V}\)
4. \(2\times 10^{-3}~\text{V}\)