MENU
Question -

An LC circuitcontains a 20 mH inductor and a 50 μF capacitor with an initial charge of 10mC. The resistance of the circuit is negligible. Let the instant the circuit isclosed be = 0.

(a) What isthe total energy stored initially? Is it conserved during LC oscillations?

(b) What isthe natural frequency of the circuit?

(c) At whattime is the energy stored

(i) completely electrical (i.e.,stored in the capacitor)? (ii) completely magnetic (i.e., stored in theinductor)?

(d) At whattimes is the total energy shared equally between the inductor and thecapacitor?

(e) If aresistor is inserted in the circuit, how much energy is eventually dissipatedas heat?



Answer -

Inductance of the inductor, L =20 mH = 20 × 10−3 H

Capacitance of thecapacitor, C = 50 μF = 50 × 10−6 F

Initial charge on thecapacitor, Q = 10 mC = 10 × 10−3 C

(a) Total energy storedinitially in the circuit is given a

Hence, the total energy stored inthe LC circuit will be conserved because there is no resistorconnected in the circuit.

(b)Naturalfrequency of the circuit is given by the relation,

Natural angular frequency,

Hence, the natural frequency ofthe circuit is 103 rad/s.

(c) (i) For time period (T), total charge on the capacitor at time t

For energy stored is electrical,we can write Q’ = Q.

Hence,it can be inferred that the energy stored in the capacitor is completelyelectrical at time, t =

(ii) Magneticenergy is the maximum when electrical energy, Q′ is equal to 0.

Hence,it can be inferred that the energy stored in the capacitor is completelymagnetic at time, 

(d) Q1 =Charge on the capacitor when total energy is equally shared between thecapacitor and the inductor at time t.

When total energy is equallyshared between the inductor and capacitor, the energy stored in the capacitor= (maximum energy).

Hence, total energy is equally shared between theinductor and the capacity at time,

(e) Ifa resistor is inserted in the circuit, then total initial energy is dissipatedas heat energy in the circuit. The resistance damps out the LC oscillation.

Comment(S)

Show all Coment

Leave a Comment

Free - Previous Years Question Papers
Any questions? Ask us!
×