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A universal motor is used in hand tools and appliances because it

  • A.runs at exactly synchronous speed whatever load is placed upon it
  • B.requires no commutator or brushes of any kind
  • C.has the highest efficiency of any small machine
  • D.gives high speed and high starting torque from a small frame

Answer: D

Speeds of ten or twenty thousand revolutions a minute from a machine that fits in the hand are what drills and vacuum cleaners need. Brush wear and acoustic noise are the price, and brushless machines have displaced it in newer products.

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