The r.m.s. value of the potential difference V shown in the figure is:
1.
2.
3.
4.
A coil has a resistance of \(30~ \mathrm{ohm}\) and inductive reactance of \(20 ~\mathrm{ohm}\) at a \(50~\mathrm{ Hz}\) frequency. If an \(\mathrm{ac}\) source of \(200 ~\mathrm{volts,}\) \(100~\mathrm{ Hz}\) is connected across the coil, the current in the coil will be:
1. | \(2.0~\mathrm{ A}\) | 2. | \(4.0~\mathrm{ A}\) |
3. | \(8.0~\mathrm{ A}\) | 4. | \(20/\sqrt{13}~\mathrm{A}\) |
The instantaneous values of alternating current and voltages in a circuit are given as,
\(i=\frac{1}{\sqrt{2}}sin\left ( 100\pi t \right )~Ampere\)
\(e=\frac{1}{\sqrt{2}}\left ( 100\pi t+\pi /3 \right )~Volt\)
What is the average power consumed by the circuit in watts?
1. | \( \frac{\sqrt{3}}{4} \) | 2. | \( \frac{1}{2} \) |
3. | \( \frac{1}{8} \) | 4. | \( \frac{1}{4}\) |
1. | \(20~\mathrm{V}\) and \(2.0~\mathrm{mA}\) |
2. | \(10~\mathrm{V}\) and \(0.5~\mathrm{mA}\) |
3. | zero and therefore no current |
4. | \(20~\mathrm{V}\) and \(0.5~\mathrm{mA}\) |
A coil of inductive reactance \(31~\Omega\) has a resistance of
\(8~\Omega\). It is placed in series with a condenser of capacitive reactance \(25~\Omega\). The combination is connected to an a.c. source of
\(110~\text{V}\). The power factor of the circuit is:
1. \(0.56\)
2. \(0.64\)
3. \(0.80\)
4. \(0.33\)
The core of a transformer is laminated so that:
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. | the ratio of voltage in primary and secondary may be increased |
A transformer is used to light a \(100\) W and \(110\) V lamp from a \(220\) V main. If the main current is \(0.5\) A, the efficiency of the transformer is approximately:
1. \(30\%\)
2. \(50\%\)
3. \(90\%\)
4. \(10\%\)
What is the value of inductance L for which the current is maximum in a series LCR circuit with C = 10 μF and ω=1000 s-1?
1. 100 mH
2. 1 mH
3. cannot be calculated unless R is known
4. 10 mH
In an AC circuit, the emf (e) and the current (I) at any instant are given respectively by
e = E0sint
I = I0sin
The average power in the circuit over one cycle of AC is:
1.
2.
3.
4.
The power dissipated in an L-C-R series circuit connected to an AC source of emf E is: