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An unfinished moving iron voltmeter is used to measure the voltage in an a.c. circuit. If a stray d.c. magnetic field having a component along the axis of the meter coil appears, the meter reading would be
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- unaffected
- decreased
- increased
- either decreased or increased depending on the direction of the d.c. field.
Correct Option: D
The meter reading will either decrease or increase depending upon the direction of flux. 
As shown in figure let FM be the flux due to meter coil and F, is due to stray magnetic field, then resultant will be F. Similarly when F is in opposite direction. Thus the reading will either increase or decrease.
