Question

Two cells of emf 1v, 2v and internal resistance 2 ohms and 1 ohms respectively are connected 1. in series 2. in parallel. what should be the external resistance in the circuit so that the current throught the resistance be the same in the two cases?

Answer 1

Of which class is it

Answer 2

Answer:

2.25R

Explanation:

In series connection,

effective EMF = 1V+2V = 3V

effective internal resistance= 3 ohm

Net Resistance= (3+R) ohm

$i = \frac{v }{r}$

so,

$i1 = \frac{3v }{3 + r}$

In parallel connection,

effective EMF = (5/3)V

net Resistance = (2/3)+R

again putting above formula,

$i2 = \frac{ \frac{5}{3} v}{ \frac{2}{3} + r }$

now according to question,

i1 = i2

on solving it,

R= 2.25 ohm

****in formulas the "R" is denoted as "r" ******