A. Remain constant
B. Increase four times
C. Become twice
D. Reduce by 50%
Answer: A. Remain constant
Explanation:
CONCEPT: EMF Equation of DC Generator
- The
EMF generated in a DC generator is given by:
Where:
= flux per
pole
= total
armature conductors
= speed in
rpm
= number of
poles
= number of
parallel paths
Special Property of Lap Winding
- In
a lap-wound DC generator:
- That
means:
- Number
of parallel paths = Number of poles
Substitution in EMF Equation
- Substituting in the EMF
equation:
- Cancelling from
numerator and denominator:
Key Observation
- The
simplified EMF equation does not contain P.
- Hence,
the generated EMF in a lap-wound generator is independent of the
number of poles.
Effect of Doubling the Number of Poles
- If
the number of poles is doubled:
- Parallel
paths are also doubled
- The
increase in poles is exactly cancelled by the increase in
parallel paths
- Therefore, no
change occurs in the generated EMF.
Why Other Options Are Incorrect
B. Increases four times ❌
- EMF
does not increase four times because cancels
with in lap
winding.
C. Becomes twice ❌
- This
would be true for a wave-wound generator, where:
- In
wave winding, EMF is proportional to .
D. Reduces by 50% ❌
- There
is no reduction in EMF since the effective EMF equation remains unchanged.
FINAL ANSWER
✅ Correct option: A —
Remains constant
✔️ Key One-Line Exam Statement
In a lap-wound DC generator, EMF is independent of the
number of poles because the number of parallel paths equals the number of
poles.