NCERT Physics Class 12 Exemplar Ch 7 Alternating Current Part 3 (For CBSE, ICSE, IAS, NET, NRA 2023)

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Short Answer

21 A device ‘X’ is connected to an a. c source. The variation of voltage, current and power in one complete cycle is shown in Figure.

(a) Which curve shows power consumption over a full cycle?

(b) What is the average power consumption over a cycle?

(c) Identify the device ‘X’ .

Device ‘X’ Connected to an a. C Source


  • A
  • Zero
  • L or C or LC

22 Both alternating current and direct current are measured in amperes. But how is the ampere defined for an alternating current?


  • An a. c current changes direction with the source frequency and the attractive force would average to zero.
  • Thus, the a. c ampere must be defined in terms of some property that is independent of the direction of current.
  • Joule՚s heating effect is such property and hence it is used to define rms value of a. c.

23 A coil of 0.01 Henry inductance and 1 ohm resistance is connected to 200 volt, 50 Hz ac supply. Find the impedance of the circuit and time lag between max. Alternating voltage and current.

24 A 60 W load is connected to the secondary of a transformer whose primary draws line voltage. If a current of 0.54 A flows in the load, what is the current in the primary coil? Comment on the type of transformer being used.


The transformer is step-down and has input voltage.

Hence .