The direction of induced emf in a DC generator is given by

 1. The basic principle of a DC generator is—

A) Coulomb’s law
B) Faraday’s laws of electromagnetic induction
C) Lenz’s law
D) Ampere’s law
✅ Answer: B
Explanation: A DC generator works on Faraday’s law of electromagnetic induction, which states that an emf is induced when a conductor cuts magnetic flux.

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2. The energy conversion in a DC generator is—
A) Electrical to Mechanical
B) Mechanical to Electrical
C) Chemical to Electrical
D) Thermal to Electrical
✅ Answer: B
Explanation: In a DC generator, the prime mover provides mechanical energy which is converted into electrical energy.

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3. The part of the DC generator which converts AC into DC is—
A) Field winding
B) Commutator
C) Armature winding
D) Brush
✅ Answer: B
Explanation: The commutator acts as a mechanical rectifier converting the alternating emf induced in the armature to unidirectional (DC) output.

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4. The function of brushes in a DC generator is to—
A) Collect current from commutator
B) Produce magnetic field
C) Support the armature
D) Provide cooling
✅ Answer: A
Explanation: Brushes are made of carbon and used to collect current from the commutator to the external circuit.

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5. The material used for brushes in DC machines is usually—
A) Copper
B) Aluminum
C) Carbon or Graphite
D) Iron
✅ Answer: C
Explanation: Carbon brushes are used because they provide good conductivity and self-lubrication.

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6. The armature core of a DC generator is laminated to—
A) Reduce copper losses
B) Reduce eddy current losses
C) Reduce hysteresis losses
D) Increase mechanical strength
✅ Answer: B
Explanation: Laminating the core minimizes eddy current losses.

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7. The emf equation of a DC generator is—
A) $E = (PΦZN) / (60A)$
B) $E = (PZN) / (60ΦA)$
C) $E = (ΦZN) / (60P)$
D) $E = (60A) / (PΦZN)$
✅ Answer: A
Explanation:
$E = \frac{PΦZN}{60A}$,
where P = poles, Φ = flux per pole, Z = total conductors, N = speed (rpm), A = parallel paths.

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8. In a DC generator, the residual magnetism is—
A) Necessary for self-excitation
B) Harmful for machine operation
C) Removed by short-circuiting
D) Constant during operation
✅ Answer: A
Explanation: Residual magnetism provides the initial emf required for self-excitation.

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9. The direction of induced emf in a DC generator is given by—
A) Fleming’s right-hand rule
B) Fleming’s left-hand rule
C) Lenz’s law
D) Joule’s law
✅ Answer: A
Explanation: Fleming’s right-hand rule gives the direction of induced emf in a generator.

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10. The main types of DC generators are—
A) Shunt, Series, Compound
B) Lap, Wave, Ring
C) Core, Shell, Toroidal
D) Inductive, Capacitive, Resistive
✅ Answer: A
Explanation: DC generators are classified based on field winding connections into Shunt, Series, and Compound types.