Question

Two 100 V full scale PMMC type DC voltmeters having sensitivity of $2k\Omega /Vand4k\Omega /V$ are connected in series. The series combination can be used to measure a dc voltage of _________V.

• A. 100 V
• B. 200 V
• C. 150 V
• D. 160 V

Answer 1

The correct option is C 150 V

Meter - 1:

$V_{fsd}=100V$

$Sensitivity=2k\Omega /V$

$R_{m1}=200k\Omega$

$I_{fsd1}=\frac{100}{200\times {10}^5}=0.5mA$

Meter-2:

$V_{fsd}=100V$

$Sensitivity=4k\Omega /V$

$R_{m1}=400k\Omega$

$I_{fsd1}=\frac{100}{400\times {10}^3}=0.25mA$


$I=min[I_{fsd1},I_{fsd2}]$

$=0.25mA$

$V=I\times 600\times {10}^3$

$=0.25\times 600\times {10}^{-3}\times {10}^3=150V$