Physics Class 12 NCERT Solutions: Chapter 7 Alternating Current Part 6

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Impedance triangle

Impedance Triangle

Q: 15. A capacitor in series with a resistance is connected to a supply.

(A) What is the maximum current in the circuit?

(B) What is the time lag between the current maximum and the voltage maximum?

Answer:

Capacitance of the capacitor,

Resistance of the resistor,

Supply voltage,

(a) Frequency of oscillations,

Angular frequency,

For a circuit, we have the relation for impedance as:

Peak voltage,

Maximum current is given as:

(B) In a capacitor circuit, the voltage lags behind the current by a phase angle of. This angle is given by the relation:

Hence, the time lag between maximum current and maximum voltage is 1.55 ms.

Q: 16. Obtain the answers to (a) and (b) in Exercise 15 if the circuit is connected to a supply? Hence, explain the statement that a capacitor is a conductor at very high frequencies. Compare this behavior with that of a capacitor in a circuit after the steady state.

Answer:

Capacitance of the capacitor,

Resistance of the resistor,

Supply voltage,

Frequency of the supply,

Angular Frequency,

Peak voltage,

Maximum current,

For an circuit, the voltage lags behind the current by a phase angle of given as:

Hence, tends to become zero at high frequencies. At a high frequency, capacitor acts as a conductor.

In a dc circuit, after the steady state is achieved. Hence, capacitor amounts to an open circuit.