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. |
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. |
I: | A small magnet takes a longer time in falling into a hollow metallic tube without touching the wall. |
II: | There is an opposition to motion due to the production of eddy currents in a metallic tube. |
Choose the correct option for the above statements:
1. | Both I and II are true and II is the correct explanation for I. |
2. | Both I and II are true and II is not the correct explanation for I. |
3. | I is true but II is false. |
4. | I is false but II is true. |
A coil is wound of a frame of rectangular cross-section. If the linear dimensions of the frame are doubled and the number of turns per unit length of the coil remains the same, then the self inductance increases by a factor of:
1. | 6 | 2. | 12 |
3. | 8 | 4. | 16 |
An aeroplane in which the distance between the tips of wings is 50 m is flying horizontally with a speed of 360 km/hr over a place where the vertical component of earth magnetic field is . The potential difference between the tips of wings would be:
1. | 0.1 V | 2. | 1.0 V |
3. | 0.2 V | 4. | 0.01 V |
The back emf induced in a coil, when current changes from 1 ampere to zero in one milli-second, is 4 volts. The self-inductance of the coil is:
1.
2.
3.
4.
A series combination of inductance (L) and resistance (R) is connected to a battery of emf E. The final value of current depends on:
1. L and R
2. E and R
3. E and L
4. E, L, and R
A uniform magnetic field of induction is confined to a cylindrical region of radius . The magnetic field is increasing at a constant rate of (tesla/second). An electron of charge , placed at the point on the periphery of the field experiences an acceleration of:
1. | \(\frac{\mathrm{B}}{(\sqrt{2}+1) \mathrm{r}}\) towards left. |
2. | \(\frac{1}{2} \frac{\mathrm{eR}}{\mathrm{m}} \frac{\mathrm{dB}}{\mathrm{dt}}\) towards right. |
3. | \(\frac{\mathrm{eR}}{2 \mathrm{~m}} \frac{\mathrm{dB}}{\mathrm{dt}}\) towards left. |
4. | zero. |
A coil has 1,000 turns and 500 as its area. The plane of the coil is placed at right angles to a magnetic field of . The coil is rotated through \(180^{0}\) in 0.2 seconds. The average e.m.f. induced in the coil, in milli-volts, is:
1. | 5 | 2. | 10 |
3. | 15 | 4. | 20 |