Physics Class 12 NCERT Solutions: Chapter 7 Alternating Current Part 5 (For CBSE, ICSE, IAS, NET, NRA 2022)

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Phase Angle in LCR Circuit

Q: 13. A coil of inductance and resistance is connected to a , ac supply.

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

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

Answer:

Inductance of the inductor,

Resistance of the resistor,

Potential of the supply voltage,

Frequency of the supply,

(A) Peak voltage is given as:

Angular frequency of the supply,

Maximum current in the circuit is given as:

(B) Equation for voltage is given as:

Equation for current is given as:

Where,

Phase difference between voltage and current

At time .

For ,

Hence, the time lag between maximum voltage and maximum current is . Now, phase angle is given by the relation,

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

Q: 14. Obtain the answers (A) to (B) Exercise 13 if the circuit is connected to a high frequency supply . Hence, explain the statement that at very high frequency, an inductor in a circuit nearly amounts to an open circuit. How does an inductor behave in a dc circuit after the steady state?

Answer:

Inductance of the inductor,

Resistance of the resistor,

Potential of the supply voltages,

Frequency of the supply,

Angular frequency,

(A) Peak voltage,

Maximum current,

(B) For phase difference , we have the relation:

It can be observed that is very small in this case. Hence, at high frequencies, the inductor amounts to an open circuit.

In a dc circuit, after a steady state is achieved . Hence, inductor L behaves like a pure conducting object.