Question

Two identical cells either in series or parallel in combination give tge same current of 0.5A through an external resistance of 4 ohms. Find the emf and internal resistance of each cell

Answer 1

Given:

The current in the circuit I= 0.5 A

The external resistance R=4

To find:

The emf and internal resistance of each cell

Solution:

The voltage in the series be V+V= 2v

The voltage in parallel be  V as it remain same for all

Resistance in series R+R=2R

Resistance in parallel R/2

Now the current in series

I= 2V/(2R+4)

Current in parallel

I= V/(R/2 + 4)

Equating the above equations

2V/(2R+ 4)= V/(R/2+ 4)

R+8=2R+4

R= 4 ohm

Now calculate the emf:

The formula for emf be

E=I(R+r)

E=0.5(4+4)

E=4V

So, the emf is 4V and the internal resistance R=4 ohm