1. | AC cannot pass through DC Ammeter. |
2. | AC changes direction. |
3. | Average value of current for the complete cycle is zero. |
4. | DC Ammeter will get damaged. |
In an L-R circuit, the inductive reactance is equal to the resistance R of the circuit. An emf of E = E0cos(ωt) is applied to the circuit. The power consumed by the circuit is:
1.
2.
3.
4.
A series AC circuit has a resistance of \(4~\Omega\) and an inductor of reactance \(3~\Omega\). The impedance of the circuit is \(z_1\). Now when a capacitor of reactance \(6~\Omega\) is connected in series with the above combination, the impedance becomes \(z_2\). Then \(\frac{z_1}{z_2}\) will be:
1. \(1:1\)
2. \(5:4\)
3. \(4:5\)
4. \(2:1\)
An inductor (L) and resistance (R) are connected in series with an AC source. The phase difference between voltage (V) and current (i) is . If the phase difference between V and i remains the same, then the capacitive reactance and impedance of the L-C-R circuit will be:
1. 2R, R
2. R, R
3. R, R
4. 2R, R
(a) | use more turns of wire in the coil. |
(b) | use thicker wire. |
(c) | change the speed of rotation. |
1. | (c) only |
2. | (a), (b) and (c) |
3. | (a) and (b) only |
4. | (a) and (c) only |
1. | \(10\) mH |
2. | \(100\) mH |
3. | \(1\) mH |
4. | Cannot be calculated unless \(R\) is known |
A \(50\) Hz ac source of \(20\) volts is connected across \(R\) and \(C\) as shown in the figure below.
If the voltage across \(R\) is \(12\) volts, then the voltage across \(C\) will be:
1. | \(8\) V |
2. | \(16\) V |
3. | \(10\) V |
4. | not possible to determine unless values of \(R\) and \(C\) are given |
A transformer has an efficiency of 90% when working on a 200 V and 3 kW power supply. If the current in the secondary coil is 6 A, the voltage across the secondary coil and the current in the primary coil, respectively, are:
1. 300 V, 15 A
2. 450 V, 15 A
3. 450 V, 13.5 A
4. 600 V, 15 A
The core of a transformer is laminated because:
1. | Energy losses due to eddy currents may be minimized |
2. | The weight of the transformer may be reduced |
3. | Rusting of the core may be prevented |
4. | Ratio of voltage in primary and secondary may be increased |
How much power is dissipated in an \(\mathrm{L-C-R}\) series circuit connected to an \(\mathrm{AC}\) source of emf \(\mathrm E\)?
1. | \(\frac{\varepsilon^{2} R}{\left[R^{2}+\left(L \omega-\frac{1}{C \omega}\right)^{2}\right]}\) | 2. | \(\frac{\varepsilon^{2} \sqrt{R^{2}+\left(L \omega-\frac{1}{C \omega}\right)^{2}}}{R}\) |
3. | \(\frac{\varepsilon^{2}\left[R^{2}+\left(L \omega-\frac{1}{C \omega}\right)^{2}\right]}{R}\) | 4. | \(\frac{\varepsilon^{2}R}{\sqrt{R^{2}+\left(L \omega-\frac{1}{C \omega}\right)^{2}}}\) |