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The detector of a bridge working at audio frequency is commonly

  • A.an electrostatic voltmeter
  • B.a pair of headphones
  • C.a moving coil galvanometer with its scale marked from a central zero position
  • D.a permanent magnet moving coil voltmeter reading the unbalance directly in volts

Answer: B

The ear is remarkably good at detecting a minimum of tone, and headphones need no supply. Where greater sensitivity or a record is wanted, a tuned amplifier feeding an indicator or an oscilloscope is used instead. A moving coil galvanometer cannot respond to alternating unbalance at all.

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