Question

Three voltmeters are connected as shown.


A potential difference has been applied across $A$ and $B$. On closing the switch $S$, what will be the effect on the readings of voltmeters ?

• A. $V_1$ increases
• B. $V_2$ decreases
• C. $V_2$ and $V_3$ both increase
• D. One of $V_2$ and $V_3$ increases and the other decreases

Answer 1

The correct option is C $V_2$ and $V_3$ both increase

Initially, when switch is open, $V_2$ and $V_3$ will be out of circuit or they are short-circuited. So no potential difference across $V_2$ and $V_3$.

Upon closing the switch, all three voltmeters will be in parallel. Now, there is some potential difference across $V_2$ and $V_3$. So potential difference across $V_2$ and $V_3$ increases and potential difference across $V_1$ remains the same.

Hence, option (c) is the correct answer.

Key concept: When voltmeters are short-circuited then potential difference across them is $0\text{volt}$.