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A shunt resistor used to measure a wide current range is problematic because

  • A.a shunt cannot measure currents below a milliampere at all
  • B.the voltage across it is in phase with the supply ripple
  • C.a value giving a usable voltage at microamperes drops too much at milliamperes
  • D.the resistance of the shunt itself changes with the current passing through it

Answer: C

A hundred-ohm shunt gives a readable millivolt at ten microamperes and a whole volt at ten milliamperes, which the design cannot tolerate. Instruments for this work switch ranges automatically or use several shunts, which is why they are not ordinary meters.

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