question_answer

A d. c. supply of 120V is connected to a large resistance X. A voltmeter of resistance \[10\,k\Omega \] placed in series in the circuit reads 4V. What is the value of X?

A)  \[190\,k\Omega \]                     

B)  \[90\,k\Omega \]

C)  \[290\,k\Omega \]                     

D)  \[390\,k\Omega \]

Correct Answer: C

Solution :

 Given \[(10\,k\Omega )I=4V\] OR\[10\,k\Omega \]. \[\frac{120V}{X+10k\Omega }=4V\] OR  \[300k\Omega =X+10k\Omega ;\] \[X=2901\,k\Omega \]