Answer to Question #347625 in Electrical Engineering for joy

Question

Two equal resistors of 15 kΩ each are connected in series across a 120 V source. A voltmeter when connected across each read 48 V in each case. Determine the resistance of the voltmeter.

Answer 1

$R_{eq}=\frac{15*R}{15+R}+15$

$I=\frac{V}{R_{eq}}=\frac{120}{\frac{15*R}{15+R}+15}$

$V_{ab}=120-I*15$

$48=120-\frac{120}{\frac{15*R}{15+R}+15}=120(1-\frac{15+R}{30R+225})$

$\frac{15+R}{30R+225}=0.6$

$18R-135=15+R$

$R=8.8\:\Omega$