Question

Which of the following statements is correct about the circuit shown in figure where 1 ohm and 0.5 ohm are the internal resistances of the 6 V and 12 V batteries respectively?

• A. The potential at point P is 6 V
• B. The potential at point Q is +0.5 V
• C. If a voltmeter is connected across the 6 V battery it will read 7 V
• D. If a voltmeter is connected across the 6 V battery it will read 5 V

Answer 1

The correct option is C If a voltmeter is connected across the 6 V battery it will read 7 V

Total resistance = 4 + 1 + 0.5 + 0.5 = 6 ohm
Net voltage in the circuit is 6 V
Current $l=\frac{6}{6}=1A$ in the anticlockwise direction
$V_{PR}=1\times 4=4V$
Since R is connected to earth $V_R=0$ hence $V_p=4V$
$V_{SQ}=0.5\times 1=0.5V$
S is at a higher potential than Q
$V_Q=-0.5V$
Current is being forced into the 6 V battery in the opposite direction.Hence $V_6=E+l_r=6+1X$
1 = 7 V