Alternating Current Physics - Alternating Current

In an AC series circuit, the instantaneous current is zero when the instantaneous voltage is maximum. Connected to the source may be a:

1. Pure inductor.
2. Pure capacitor.
3. Pure resistor.
4. Combination of an inductor and a capacitor.

The magnetic field energy in an inductor changes from maximum value to minimum value in 5.0ms when connected to an AC source. The frequency of the source:

1. 20Hz.
2. 50Hz.
3. 200Hz.
4. 500Hz.

To convert mechanical energy into electrical energy, one can use:

1. DC dynamo.
2. AC dynamo.
3. Motor.
4. Transformer.

Transformers are used:

1. In DC circuits only.
2. In AC circuits only.
3. In both DC and AC circuits.
4. Neither in DC nor in AC circuits.

The AC voltage across a resistance can be measured using:

1. A potentiometer.
2. A hot-wire voltmeter.
3. A moving-coil galvanometer.
4. A moving-magnet galvanometer.

An AC source is connected to a capacitor. Will the rms current increase, decrease or remain constant if a dielectric slab is inserted into the capacitor?

Can a hot-wire ammeter be used to measure a direct current having a constant value? Do we have to change the graduations?

In a circuit containing a capacitor and an AC source the current is zero at the. stant the source voltage is maximum. Is it consistent with Ohm's law?

Can the peak voltage across the inductor be greater than the peak voltage of the source in an LCR circuit?

A transformer is designed to convert an AC voltage of 220V to an AC voltage of 12V. If the input terminals are connected to a DC voltage of 220V, the transformer usually burns. Explain.

The peak power consumed by a resistive coil, when connected to an AC source, is 80W. Find the energy consumed by the coil in 100 seconds, which is many times larger than the time period of the source.

A resistance is connected to an AC source. If a capacitor is included in the series circuit, will the average power absorbed by the resistance increase or decrease? If an inductor of small inductance is also included in the series circuit, will the average power absorbed increase or decrease further?

The dielectric strength of air is 3.0 × 10⁶V/m. A parallel-plate air-capacitor has area 20cm² and plate separation 0.10mm. Find the maximum rms voltage of an AC source that can be safely connected to this capacitor.

Figure shows a typical circuit for a low-pass filter. An AC input V_i = 10mV is applied at the left end and the output V₀ is received at the right end. Find the output voltage for ν = 10kHz, 1.0MHz and 10.0MHz. Note that as the frequency is increased the output decreases and, hence, the name low-pass filter.

A transformer has 50 turns in the primary and 100 in the secondary. If the primary is connected to a 220V DC supply, what will be the voltage across the secondary?

The household supply of electricity is at 220V (rms value) and 50Hz. Find the peak voltage and the least possible time in which the voltage can change from the rms value to zero.