Two cells of emf E1 and E2 are joined in opposition (such that E1>E2). If r1 and r2 be the internal resistance and R be the external resistance, then the terminal potential difference is
E1−E2r1+r2+R×R
I=Net emfTotal resistance=E1−E2R+r1+r2V=IR⇒V=(E1−E2)RR+r1+r2