The maximum value of AC voltage in a circuit is 707 V. Its rms value is

• 70.7 V

• 100 V

• 500 V

• 707 V

The resonant frequency of an LCR circuit occurs at a frequency equal to

• $\frac{1}{\mathrm{LC}}$

• $\frac{1}{\sqrt{\mathrm{LC}}}$

• $\frac{1}{\mathrm{LCR}}$

• $\frac{1}{\mathrm{CR}}$

An AC is given by i = i₁ cos ωt + i₂ sin ωt. The rrns current is given by

• $\frac{{\mathrm{i}}_1 + {\mathrm{i}}_2}{\sqrt{2}}$

• $\frac{{\mathrm{i}}_1 - {\mathrm{i}}_2}{\sqrt{2}}$

• $\sqrt{\left(\frac{{{\mathrm{i}}_1}^2 + {{\mathrm{i}}_2}^2}{2}\right)}$

• $\sqrt{\left(\frac{{{\mathrm{i}}_1}^2 - {{\mathrm{i}}_2}^2}{2}\right)}$

If a transformer of an audio amplifier has output impedance 8000 Ω and the speaker has input impedance of 8 Ω, the primary and secondary turns of this transformer connected between the output of amplifier and to loud speaker should have the ratio

• 1000 : 1

• 100 : 1

• 1 : 32

• 32 : 1

Alternating current is transmitted to distant places

• at high voltage and low current

• at high voltage and high current

• at low voltage and low current

• at low voltage and high current

In a step-up transformer the voltage in the primary is 220 V and the current is 5 A. The secondary voltage is found to be 22000 V. The current in the secondary (neglect losses) is

• 5 A

• 50 A

• 500 A

• 0.05 A

57.

In a pure inductive circuit, current

• lags behind emf by $\mathrm{\pi }/2$

• leads the emf by $\mathrm{\pi }/2$

• lags behind by $\mathrm{\pi }$

• leads the emf by $\mathrm{\pi }$

The time taken by AC of 50 Hz in reaching from zero to the maximum value is

• 50 × 10^-3 sec

• 5 × 10^-3 sec

• 1 × 10^-3 sec

• 2 × 10^-3 sec

The ratio of the secondary to the primary turns in a transformer is 3 : 2 and the output power is P. Neglecting all power losses, the input power must be

• $\frac{\mathrm{P}}{2}$

• P

• $\frac{2\mathrm{P}}{3}$

• $\frac{3\mathrm{P}}{2}$

In an LCR circuit the potential difference between the terminals of the inductance is 60 V, between the terminals of the capacitor is 30 V and that between the terminals of resistance is 40 V. The supply voltage will be equal to

• 130 V

• 10 V

• 50 V

• 70 V