NCERT Physics Class 12 Exemplar Ch 7 Alternating Current Part 1

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Vary Short Answer

14 If a LC circuit is considered analogous to a harmonically oscillating spring block system, which energy of the LC circuit would be analogous to potential energy and which one analogous to kinetic energy?


  • Magnetic energy analogous to kinetic energy and electrical energy analogous to potential energy.

15 Draw the effective equivalent circuit of the circuit shown in Figure, at very high frequencies and find the effective impedance.

Draw Effective Equivalent Circuit


  • At high frequencies, capacitor short circuit (low reactance) and inductor open circuit (high reactance) .
  • Therefore, the equivalent circuit as shown in the Figure.
Equivalent Circuit of the Circuit Shown in Figure

16 Study the circuits (a) and (b) shown in Figure and answer the following questions.

(a) Under which conditions would the rms currents in the two circuits be the same?

(b) Can the rms current in circuit (b) be larger than that in (a) ?

Conditions for Rms Currents to be Same


  • Yes, if rms voltage in the two circuits is same then at resonance, the rms current in LCR will be same as that in R circuit.
  • No, because

17 Can the instantaneous power output of an ac source ever be negative? Can the average power output be negative?


Yes, No.