(a) increased by 10%.
(b) reduced by 20%.
(c) increased by 8%.
(d) decreased by 8%.
Answer: (c) increased by 8%.
Explanation:
CONCEPT: EMF Equation of DC Generator
The generated EMF of a DC generator is given by:
Where:
= Generated
voltage
= Flux per pole
= Speed
= Constant
So,
This means:
👉 Voltage is directly
proportional to flux and speed.
STEP 1: Initial Conditions
Let:
Initial voltage = 
V
Initial flux = 
Initial speed = 
So,
STEP 2: New Conditions
New Speed
Speed increased by 20%:
New Flux
Flux reduced by 10%:
STEP 3: New Voltage Calculation
Using EMF equation:
Substitute values:
STEP 4: Substitute Initial Voltage
STEP 5: Percentage Change
FINAL ANSWER
✔ Voltage increases by 8%
Correct Option
✅ (c) Increased by 8%
KEY EXAM POINT ⭐
For DC generator:
So,
Use this formula directly in numericals.
ONE-LINE CONCLUSION
When speed increases by 20% and flux decreases by 10%, the
net effect is an 8% increase in generated voltage.