Three moving iron type voltmeters are connected as shown below. Voltmeter readings are $V$, $V1$ and $V2$ , as indicated. The correct relation among the voltmeter readings is
1. $V=\dfrac{V1}{\sqrt{2}}+\dfrac{V2}{\sqrt{2}}$
2. $V =V_1 +V_2$
3. $V =V_1V_2$
4. $V =V_2 - V_1$