Question

The circuit shown below incorporates a permanent magnet coil milli-ammeter of range 0-1 mA having a series resistance of $10k\Omega .$ Assuming constant diode forward resistance of $50k\Omega ,$ a forward diode drop of 0.7 V and infinite reverse diode resistance for each diode, the reading of the meter in mA is

• A. 0.45
• B. 0.5
• C. 0.7
• D. 0.9

Answer 1

The correct option is A 0.45

Current in the inverting arm

$I_m=\frac{5\sqrt{2}-0}{{10}^4}=0.707mA$

PMMC measures the average value

$=\frac{2I_m}{\pi }=\frac{2\times 0.707}{\pi }=0.45mA$