Two batteries one of the emf `3V`, internal resistance `1Omega` and the other of emf `15 V`, internal resistance `2Omega` are connected in series with a resistance `R` as shown. If the potential difference between points a and b is zero, the resistance `R` in `Omega` is

Options

A. 5
B. 7
C. 3
D. 1

Answer

C

Explanation

`E-ir=0`
`:. 3-((3+15)/(1+2+R))(1)=0`
Solving this equation we get
`R=3Omega`