An electric circuit is shown in the figure. Calculate the potential . . .

Question : An electric circuit is shown in the figure. Calculate the potential difference across the resistor of 400 Ohm, as will be measured by the voltmeter V of resistance 400 Ohm.

Doubt by Mohini 

Solution : 
If we look closer than we can see that 400 Ω resistor and 400 Ω voltmeter both are connected in parallel so their equivalent resistance would be 
=(400×400)/(400+400)
=(400×400)/800
= 200 Ω

Now If we drawn the equivalent diagram of the circuit then we realise that it becomes a balanced wheat stone bridge as shown below.
 

Now the equivalent resistance of balanced wheat stone bridge would be 
Req=(300×300)/(300+300)
Req=(300×300)/600
Req = 150 Ω

Current drawn from the battery, I = V/Req
I = 10/150
I = (1/15) A
Current through ABC or Current through ADC = I/2
= (1/15)/2
= (1/30) A

Now, Voltage drop across the branch BC 
= current × Resistance (BC)
= (1/30)×200
=20/3 V
=6.666 V
= 6.67 V