(a) flux linking with the coil is maximum.
(b) rate of change of flux linkage is minimum.
(c) rate of change of flux linkage is maximum.
(d) rate of cutting flux by the coil sides is minimum.
Answer: (c) rate of change of flux linkage is maximum.
Explanation:
CONCEPT: Electromagnetic Induction
- The
induced EMF in a coil is governed by Faraday’s Law of
Electromagnetic Induction.
- According
to Faraday’s law, the magnitude of induced EMF depends on the rate
of change of magnetic flux linkage.
Faraday’s Law
- Faraday’s
law is given by:
Where:
= induced EMF
= number of turns
= magnetic flux
= rate of change
of magnetic flux
- Hence:
- EMF
∝ rate of change of flux linkage
Flux Linkage in a Rotating Coil
- Magnetic
flux through the coil is:
Where:
= magnetic field
strength
= area of the
coil
= angle between
magnetic field and normal to the coil
Explanation of EMF Variation
- When
the plane of the coil is parallel to the magnetic field:
- Flux
is zero
- But
the rate of change of flux is maximum
- At
this position, the coil cuts magnetic field lines at the highest
speed.
- When
the plane of the coil is perpendicular to the magnetic field:
- Flux
is maximum
- Rate
of change of flux is zero
- Hence
EMF is zero
Key Reason
- Induced
EMF depends not on the magnitude of flux, but on how
fast the flux changes.
- Therefore,
EMF becomes maximum when:
Final Answer
✅ Correct option: (c)
Rate of change of flux linkage is maximum
One-Line Exam Statement
Induced EMF in a rotating coil is maximum when the rate
of change of magnetic flux linkage is maximum.
Important Exam Notes
- Maximum
flux ≠ Maximum EMF
- Zero
flux ≠ Zero EMF
- EMF
depends only on rate of change of flux
- Coil
plane ∥ magnetic field → maximum
EMF