Question

Match List - I with List - II.

List - I	List - II
A. Three Phase Induction Motor B. Three Phase Alternator C. Transformer D. Single phase Induction Motor	I. Constant Frequency II. Not self starting III. Always runs at less than synchronous speed IV. Always runs at synchronous speed

• A. A-III, B-IV, C-I, D-I
• B. A-III, B-IV, C-I, D-II
• C. A-IV, B-III, C-I, D-II
• D. A-IV, B-II, C-III, D-I

Hint:

Important machine properties: \[ \text{3-}\phi \text{ induction motor} \rightarrow \text{speed below } N_s \] \[ \text{Alternator} \rightarrow \text{synchronous speed} \] \[ \text{Single phase induction motor} \rightarrow \text{not self starting} \]

Answer 1

The Correct Option is B

Concept: Each electrical machine has a unique operating characteristic. This question checks conceptual understanding of:
• induction motors,
• alternators,
• transformers,
• single phase motors.

Step 1: Matching Three Phase Induction Motor. A three phase induction motor always operates: \[ \text{below synchronous speed} \] because slip is necessary for torque production. If rotor speed becomes equal to synchronous speed: \[ \text{relative motion becomes zero} \] and torque disappears. Hence: \[ A \rightarrow III \]

Step 2: Matching Three Phase Alternator. Alternator rotor rotates exactly at: \[ \text{synchronous speed} \] given by: \[ N_s=\frac{120f}{P} \] Hence: \[ B \rightarrow IV \]

Step 3: Matching Transformer. Transformer works on electromagnetic induction and operates only with: \[ \text{constant frequency AC supply} \] Frequency change affects:
• flux,
• core losses,
• induced emf. Therefore: \[ C \rightarrow I \]

Step 4: Matching Single Phase Induction Motor. Single phase induction motor is: \[ \text{not self starting} \] because single phase supply produces pulsating magnetic field rather than rotating magnetic field. Hence: \[ D \rightarrow II \]

Step 5: Writing the complete matching. Thus: \[ A-III,\quad B-IV,\quad C-I,\quad D-II \]

Step 6: Selecting the correct option. Hence correct option is: \[ \boxed{(2)} \]