Question

Given below are two statements, one labelled as Assertion (A) and the other labelled as Reason (R).

Assertion (A): The current drawn by the motor lags behind the voltage applied.
Reason (R): Motor is an inductive load.

In light of the above statements, choose the correct answer from the options given below.

• A. Both (A) and (R) are true and (R) is the correct explanation of (A).
• B. Both (A) and (R) are true but (R) is not the correct explanation of (A).
• C. (A) is true but (R) is false.
• D. (A) is false but (R) is true.

Hint:

Think about what property of a motor winding causes a phase difference between voltage and current.

Answer 1

The Correct Option is A

Step 1: Look at what kind of load a motor presents to the AC supply. The stator winding of a motor is a coil of wire, so besides its resistance it also has inductance. Any coil carrying alternating current opposes the change in current through it, and that opposition is what we call inductive reactance.
Step 2: In a purely resistive circuit, voltage and current rise and fall together, they are in phase. In a circuit that has inductance, the current cannot change as fast as the voltage across it, so the current waveform reaches its peak a little later than the voltage waveform. This delay is described as the current lagging the voltage by a phase angle \(\phi\), which is also the power factor angle of the load.
Step 3: Since a motor winding is an inductive load, the current it draws from the supply lags the applied voltage. This is exactly what Assertion (A) states, so (A) is true.
Step 4: Reason (R) says the motor is an inductive load. This is also true, and it is precisely the inductance of the winding that causes the lag described in (A). So (R) is not just true on its own, it is the actual physical reason behind (A).
Step 5: Check the remaining options. Option 2 would apply if R were true but unrelated to A, which is not the case here since R directly causes A. Options 3 and 4 both call one of the statements false, but both A and R are true. So the correct choice is that both (A) and (R) are true and (R) correctly explains (A).