Two cells with same emf E but different inteınal resistances, r₁ , and r₂ are connected in series to an external resistance R . If the potential difference across the first cell is zero then the value of R is

Step-by-step solution

Equivalent emf, E _ eq = E + E =2 E Equivalent resistance, R_ e q =r₁+r₂+R Current flowing through the circuit, i= 2 E r₁+r₂+R Potential drop across the first cell, V ₁= E - ir ₁ aligned & 0=E-i₁ & 0=E- ( 2 E r₁+r₂+R ) r₁ & 0=r₁+r₂+R-2 r₁ & 0=r₂-r₁+R & R=r₁-r₂ aligned