Alternating current cannot be measured by a D.C. ammeter because:
1. A.C. can not pass through D.C. Ammeter
2. A. C. changes direction
3. Average value of current for 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. $\frac{{\mathrm{E}}_0^2}{\sqrt{2}\mathrm{R}}$

2. $\frac{{\mathrm{E}}_0^2}{4\mathrm{R}}$

3. $\frac{{\mathrm{E}}_0^2}{2\mathrm{R}}$

4. $\frac{{\mathrm{E}}_0^2}{8\mathrm{R}}$

A series AC circuit has a resistance of 4 $\mathrm{\Omega }$ and an inductor of reactance 3 $\mathrm{\Omega }$. The impedance of the circuit is z₁. Now when a capacitor of reactance 6 $\mathrm{\Omega }$ is connected in series with the above combination, the impedance becomes $z_{2.}$ $\frac{{\mathrm{z}}_1}{{\mathrm{z}}_2}$ 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 $45°$. 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$\sqrt{2}$

2. R, R$\sqrt{2}$

3. R, R

4. 2R, R$\sqrt{3}$

What is the value of inductance L for which the current is a maximum in a series LCR circuit with C=10 μF and $\mathrm{\omega }$ = 1000 s^-1 ?

1. 10 mH
2. 100 mH
3. 1 mH
4. cannot be calculated unless R is known

In an ideal parallel LC circuit, the capacitor is charged by connecting it to a dc source which is then disconnected. The current in the circuit will:
1. become zero instantaneously.
2. grow monotonically.
3. decay monotonically.
4. oscillate instantaneously.

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:

How much power is dissipated in an L-C-R series circuit connected to an AC source of emf 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.  \(\frac{\varepsilon^{2}R}{\sqrt{R^{2}+\left(L \omega-\frac{1}{C \omega}\right)^{2}}}\)