Q1. A transformer works on the principle of:
A. Self-induction
B. Mutual induction
C. Static induction
D. Electrostatic induction
Correct Option: B
Explanation:
A transformer has two magnetically coupled windings. Alternating current in the primary produces alternating flux which links the secondary and induces emf due to mutual induction.
Q2. A transformer:
A. Changes frequency
B. Changes voltage only
C. Changes voltage and current keeping frequency same
D. Changes power
Correct Option: C
Explanation:
A transformer changes voltage and current levels according to the turns ratio, but frequency remains unchanged because the same alternating flux links both windings.
Q3. Transformer transfers power from one circuit to another through:
A. Electric field
B. Electrostatic induction
C. Magnetic field
D. Conduction through core
Correct Option: C
Explanation:
There is no electrical connection between windings. Power is transferred through time-varying magnetic flux in the core by mutual induction.
Q4. Which law explains induced emf in transformer windings?
A. Lenz’s law
B. Fleming right hand rule
C. Faraday’s law
D. Ampere’s law
Correct Option: C
Explanation:
Faraday’s law states that induced emf is proportional to the rate of change of magnetic flux, which is the basic operating principle of transformers.
Q5. In transformer, alternating flux is produced in:
A. Primary only
B. Secondary only
C. Air only
D. Laminated core
Correct Option: D
Explanation:
Alternating current in the primary creates alternating flux in the laminated iron core, which provides a low reluctance path linking both windings.
Q6. The frequency of secondary voltage of transformer is:
A. Greater than primary
B. Less than primary
C. Same as primary
D. Zero
Correct Option: C
Explanation:
Since the same alternating flux links both windings, the frequency of secondary voltage is equal to the supply frequency.
Q7. Laminations in transformer core are used to reduce:
A. Hysteresis loss
B. Eddy current loss
C. Copper loss
D. Leakage flux
Correct Option: B
Explanation:
Laminations increase the resistance to circulating eddy currents, thereby reducing eddy current loss.
Q8. Silicon is added to transformer core steel to:
A. Increase resistivity and decrease hysteresis loss
B. Increase permeability only
C. Decrease resistivity
D. Increase weight
Correct Option: A
Explanation:
Silicon steel increases resistivity and reduces hysteresis loop area, thereby reducing both eddy current and hysteresis losses.
Q9. The thickness of laminations in transformer core (50 Hz) is approximately:
A. 2 mm
B. 1 mm
C. 0.5 mm
D. 0.35 mm
Correct Option: D
Explanation:
For 50 Hz transformers, lamination thickness is about 0.35 mm to limit eddy currents and reduce core losses.
Q10. In core-type transformer:
A. Windings surround core
B. Core surrounds windings
C. Windings placed at bottom
D. Windings placed outside tank
Correct Option: A
Explanation:
In core-type transformers, windings are placed on the limbs and encircle the core.
Q11. In shell-type transformer:
A. Windings surround core
B. Core surrounds windings
C. Windings and core separated
D. No core used
Correct Option: B
Explanation:
In shell-type transformers, windings are placed on the central limb and are surrounded by the core.
Q12. For high-voltage, multi-winding transformer, preferred type is:
A. Core type
B. Shell type
C. Auto-transformer
D. Distribution transformer
Correct Option: B
Explanation:
Shell-type transformers offer better insulation support, lower leakage reactance, and greater mechanical strength for high-voltage multi-winding applications.
Q13. Low-voltage winding in transformer is placed near the core because:
A. It is cheaper
B. Reduces copper loss
C. Easy to cool
D. Easy to insulate
Correct Option: D
Explanation:
Low-voltage winding requires less insulation. Placing it near the core reduces insulation requirement for the high-voltage winding.
Q14. In shell-type transformer, winding used is generally:
A. Cylindrical winding
B. Spiral winding
C. Sandwich / disc winding
D. Wave winding
Correct Option: C
Explanation:
Shell-type transformers generally use disc or sandwich windings to improve cooling and withstand short-circuit forces.
Q15. Core stepping in transformers is done to:
A. Increase weight
B. Increase losses
C. Improve space factor and reduce I²R loss
D. Increase leakage flux
Correct Option: C
Explanation:
Stepped core approximates a circular cross-section, reducing mean length of turn, copper requirement, and I²R losses.
Q16. Cruciform core section is used in:
A. Small transformers
B. Medium transformers
C. Large transformers
D. Auto-transformers
Correct Option: C
Explanation:
Cruciform and multi-stepped cores are used in large power transformers to improve space factor and reduce losses.
Q17. The main function of transformer oil is:
A. Cooling only
B. Insulation only
C. Both cooling and insulation
D. Lubrication
Correct Option: C
Explanation:
Transformer oil provides electrical insulation and removes heat from windings and core by convection.
Q18. Shell-type transformers provide:
A. Less mechanical strength
B. Better support against short-circuit forces
C. Poor insulation
D. Higher noise
Correct Option: B
Explanation:
Sandwich windings and rigid clamping in shell-type transformers give better mechanical strength against short-circuit forces.
Q19. A single-phase transformer has N1 = 1000, N2 = 250, V1 = 400 V. Secondary voltage is:
A. 50 V
B. 100 V
C. 200 V
D. 1000 V
Correct Option: B
Explanation:
V2/V1 = N2/N1
⇒ V2 = 400 × (250/1000) = 100 V.
Q20. A transformer has turns ratio 10:1. Primary current is 2 A. Secondary current is:
A. 0.2 A
B. 2 A
C. 10 A
D. 20 A
Correct Option: D
Explanation:
For an ideal transformer, V1I1 = V2I2.
Current is inversely proportional to turns ratio, so secondary current = 10 × 2 = 20 A.