question_answer

The measurement of voltmeter in the following circuit is :

A) 6.0V                                      

B) 40V

C) 3.4V                                      

D) 25V

Correct Answer: D

Solution :

Key Idea: In parallel combination of resistances the potential difference between  the ends is same. The two resistances \[40\Omega \]and \[60\Omega \] are connected in parallel, since their first ends are connected to one point and second ends to  the other. \[\therefore \]        \[\frac{1}{R}=\frac{1}{{{R}_{1}}}+\frac{1}{{{R}_{2}}}\]               \[=\frac{1}{60}+\frac{1}{40}\] \[\Rightarrow \]     \[R=24\,\Omega \] In this circuit, the current is  \[\Rightarrow \]               \[i=\frac{E}{R}=\frac{6}{24}A\] Hence, potential difference across voltmeter is \[V=iR'\] \[=\frac{6}{24}\times 100=25\text{V}\]