Alternating Current

If an alternating voltage is represented as E = 141 sin (628 t), then the rms value of the voltage and the frequency are respectively

• 141 V, 628 Hz

• 100 V, 50 Hz

• 100 V, 100 Hz

• 141 V, 100 Hz

A step-down transformer is used on a 1000 V line to deliver 20 A at 120 V at the secondary coil. If the efficiency of the transformer is 80%, the current drawn from the line is

• 3 A

• 30 A

• 0.3 A

• 2.4 A

An alternating current of rms value 10 A is passed through a 12 Ω resistor. The maximum potential difference across the resistor is

• 20 V

• 90 V

• 169.68 V

• None of these

In the circuit shown below, the switch is kept in position a for a long time and is then thrown to position b. The amplitude of the resulting oscillating current is given by

• $\mathrm{E}\sqrt{\mathrm{L}/\mathrm{C}}$

• E / R

• infinity

• $\mathrm{E}\sqrt{\mathrm{C}/\mathrm{L}}$