(a) dc.
(b) ac.
(c) dc and ac both.
(d) none of these.
Answer: (b) ac.
Explanation:
CONCEPT: Induced EMF in a Magnetic Field
- When
a conductor moves or rotates in a magnetic field,
an EMF is induced according to Faraday’s law of
electromagnetic induction.
- The direction
of induced EMF depends on:
- Direction
of motion of the conductor
- Direction
of the magnetic field
Explanation of EMF Reversal
- A bipolar
magnetic field consists of North and South poles.
- As
the conductor rotates:
- It
first cuts magnetic flux under the North pole.
- Then
it moves into the region under the South pole.
- Each
time the conductor passes from one pole to the other:
- The direction
of induced EMF and current reverses.
- This
repeated reversal occurs periodically during continuous
rotation.
Nature of Induced EMF
- Since
the direction of EMF alternates with time, the induced EMF
is alternating in nature.
- Therefore,
the induced current produced in the conductor is alternating
current (AC).
DC Generator Case
- In
a DC generator, the EMF generated in the armature conductors
is internally AC.
- A
mechanical rectifier called a commutator is used to:
- Reverse
the connections every half rotation
- Convert
the internally generated AC into unidirectional (DC) output for
the external circuit.
Final Answer
✅ Correct option: (b)
Alternating current (AC)
✔️ Key One-Line Exam Statement
A rotating conductor in a stationary bipolar magnetic
field produces an alternating EMF.
Important Exam Notes
- Internal
EMF in DC generators is AC
- Commutator
converts AC → DC
- AC
is produced due to periodic reversal of EMF direction