Alternating current cannot be measured by a D.C. ammeter because:
1. | A.C. cannot pass through D.C. Ammeter |
2. | A. C. changes direction |
3. | Average value of current for the complete cycle is zero |
4. | D.C. 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 and an inductor of reactance 3 . The impedance of the circuit is z1. Now when a capacitor of reactance 6 is connected in series with the above combination, the impedance becomes 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 |
What is the value of inductance L for which the current is a maximum in a series LCR circuit with C=10 μF and = 1000 s-1?
1. | 10 mH |
2. | 100 mH |
3. | 1 mH |
4. | Cannot be calculated unless R is known |
A 50 Hz a.c. 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. | \(\frac{\varepsilon^{2}R}{\sqrt{R^{2}+\left(L \omega-\frac{1}{C \omega}\right)^{2}}}\) |