Ms. Rani decides to convert her AC generator into a DC generator. Which one of the following she would need to use ?
- A.A split-ring type commutator
- B.Slip rings and brushes
- C.A stronger magnetic field
- D.A rectangular wire loop
Correct answer
Explanation
The correct answer is A, A split-ring type commutator. A split-ring commutator reverses the coil's connection to the outer circuit every half turn, so the current outside flows in one direction only.
In any generator the coil rotating in a magnetic field produces a current that changes direction every half rotation. An AC generator passes this current out through two full slip rings, so the output alternates. In a DC generator the two full rings are replaced by one ring split into two halves. Just as the current in the coil reverses, each half of the ring changes the brush it touches, so the current in the external circuit keeps the same direction. The same split-ring device keeps an electric motor turning.
B is wrong because slip rings and brushes are what an AC generator already uses; they give alternating current.
C is wrong because a stronger magnet only raises the size of the induced current, not its direction.
D is wrong because the rectangular coil is present in both kinds of generator.
Exam tip: slip rings give AC; a split-ring commutator gives DC and is also used in the DC motor.
Practice Questions
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- A.1 and 2 only
- B.2 and 3 only
- C.1 only
- D.1, 2 and 3
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- A.0 °C
- B.-100 °C
- C.-273.15 °C
- D.-173.15 °C
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- A.the reaction requires initiation by a catalyst
- B.oxides of nitrogen are unstable
- C.the reaction is endothermic and requires very high temperature
- D.the stoichiometry of N₂ and O₂ in air is not ideal for the reaction to take place
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- A.Substitution reaction.
- B.Elimination reaction.
- C.Addition reaction.
- D.Free-radical polymerization.
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Read the full explanation →A positive charge is moving towards south in a space where magnetic field is pointing in the north direction. The moving charge will experience :
- A.a deflecting force towards north direction.
- B.a deflecting force towards east direction.
- C.a deflecting force towards west direction.
- D.no deflecting force.
Show answer
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Read the full explanation →