Multiple Choice Questions
Note: Try and then see the answer with Explanation after question sets.
1. A transformer works on which principle?
a) Faraday’s law of electromagnetic induction
b) Ohm’s law
c) Lenz’s law
d) Coulomb’s law
2. Which type of transformer is used to measure high current?
a) Potential Transformer (PT)
b) Power Transformer
c) Current Transformer (CT)
d) Distribution Transformer
3. The primary and secondary windings of a transformer are
a) Connected electrically
b) Connected magnetically
c) Connected mechanically
d) Directly connected
4. In a step-up transformer
a) Primary turns > Secondary turns
b) Secondary turns > Primary turns
c) Primary and secondary turns equal
d) Primary turns are negligible
5. The efficiency of a distribution transformer is maximum at
a) Full load
b) No load
c) 50% of full load
d) Variable with load
6. The core of a transformer is made of
a) Solid steel
b) Laminated silicon steel
c) Cast iron
d) Aluminum
7. Transformer oil is mainly used for
a) Insulation only
b) Cooling only
c) Both insulation and cooling
d) Reducing copper loss
8. Which type of loss occurs in transformer windings?
a) Eddy current loss
b) Copper loss
c) Hysteresis loss
d) Dielectric loss
9. The EMF equation of a transformer is
a) E=4.44fNϕm
b) E=Nϕ
c) E=2πfNϕm
d) E=V/I
10. Open-circuit test on a transformer is used to measure
a) Copper loss
b) Efficiency
c) Core loss (Iron loss)
d) Leakage reactance
11. Short-circuit test on a transformer is used to measure
a) Copper loss
b) Core loss
c) Efficiency directly
d) Turns ratio
12. In a transformer, voltage regulation is defined as
a) Change in efficiency with load
b) Change in secondary voltage from no-load to full-load
c) Ratio of output power to input power
d) Losses per unit load
13. Which of the following is NOT a type of transformer?
a) Auto-transformer
b) Power transformer
c) Distribution transformer
d) Rotating transformer
14. All-day efficiency of a transformer is important for
a) Power transformers
b) Distribution transformers
c) Auto-transformers
d) Instrument transformers
15. The function of a transformer is to:
a) Convert DC to AC
b) Change the frequency of AC supply
c) Step-up or Step-down AC voltage
d) Convert AC to DC
Answer
1 a) Faraday’s law of electromagnetic induction
Explanation: Transformer action is based on mutual induction which is governed by Faraday’s law of electromagnetic induction.
2 c) Current Transformer (CT)
Explanation: CTs step down high currents to measurable values for protection and metering.
3 b) Connected magnetically
Explanation: Windings are electrically isolated but magnetically coupled through the core.
4 b) Secondary turns > Primary turns
Explanation: Step-up transformer increases voltage, so secondary has more turns.
5 c) 50% of full load
Explanation: Distribution transformers are designed to operate efficiently at 50–60% load, since they run continuously near that load.
6 b) Laminated silicon steel
Explanation: Laminations reduce eddy current losses, silicon steel reduces hysteresis loss.
7 c) Both insulation and cooling
Explanation: Oil provides insulation between windings and helps remove heat from the core.
8 b) Copper loss
Explanation: Current flowing through windings causes I²R losses, known as copper losses.
9 a) E=4.44fNϕm
Explanation: The induced emf per turn is 4.44fϕm. Multiplying by turns gives emf in winding.
10 c) Core loss (Iron loss)
Explanation: In OC test, no load current is small, so copper loss negligible, only iron loss is measured.
11 a) Copper loss
Explanation: In SC test, applied voltage is low, iron loss negligible, only copper loss is measured.
12 b) Change in secondary voltage from no-load to full-load
Explanation: Voltage regulation indicates how much the secondary voltage drops under load.
13 d) Rotating transformer
Explanation: Transformer is a static device; “rotating transformer” does not exist.
14 b) Distribution transformers
Explanation: Distribution transformers run all day with varying loads, so all-day efficiency is considered.
15 c) Step-up or Step-down AC voltage
Explanation: A transformer works on the principle of mutual induction and is used to increase (step-up) or decrease (step-down) AC voltage without changing frequency.