# Two cells of same emf E but internal resistance $r_{1}$ and $r_{2}$ are connected in series to an external resistor R (Figure). What should be the value of R so that the potential difference across the terminals of the first cell becomes zero.

$EMF_{ef}=E+E=2E$

$R_{ef}=r_1+r_2$

$I=\frac{2E}{R+r_1+r_2}$

As net potential across the cell is 0,

$E-Ir_1=0$

$E-\frac{2Er_1}{R+r_1+r_2}=0$

$R=r_1-r_2$

## Similar Questions

### Preparation Products

##### Knockout NEET May 2021 (One Month)

An exhaustive E-learning program for the complete preparation of NEET..

₹ 14000/- ₹ 6999/-
##### Foundation 2021 Class 10th Maths

Master Maths with "Foundation course for class 10th" -AI Enabled Personalized Coaching -200+ Video lectures -Chapter-wise tests.

₹ 350/- ₹ 112/-
##### Knockout JEE Main April 2021 (One Month)

An exhaustive E-learning program for the complete preparation of JEE Main..

₹ 14000/- ₹ 6999/-
##### Knockout NEET May 2021

An exhaustive E-learning program for the complete preparation of NEET..

₹ 22999/- ₹ 14999/-