BSc Nursing GNM 2019 Solved Paper

Net resistance of the circuit
=r1+r2+R
Net emf in series =E+E=2E Therefore, from Ohm's law, current in the circuit,
i‌‌=‌

‌ Net emf ‌

‌ Net resistance ‌

⇒‌‌i‌‌=‌

2E

r1+r2+R

. . . (i)
It is given that, as circuit is closed, potential difference across the first cell is zero.
‌ i.e. ‌‌‌V=E−ir1=0
⇒‌‌i=‌

E

r1

. . . (ii)
On equating Eqs. (i) and (ii), we get
‌

E

r1

=‌

2E

r1+r2+R

⇒2r1=r1+r2+R
∴R=‌ external resistance ‌=r1−r2