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True or false: headphones are useless as a bridge detector at power frequency.

  • A.False, provided the headphones are of the high-impedance type used in bridge work
  • B.True, because headphones respond only to the direct component of the unbalance
  • C.True, since fifty hertz is too low for the ear to judge a minimum
  • D.False, the ear being equally sensitive at all frequencies from twenty hertz upward

Answer: C

The ear is insensitive at 50 hertz, so the null cannot be judged. A vibration galvanometer tuned to the supply frequency is used instead at power frequencies, while headphones come into their own between about five hundred and two thousand hertz where hearing is acute.

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