Question

A cell can supply currents of 0.80A and 0.40A through a 2ohms and a 3ohms resistor respectively. Calculate the internal resistance of the cell

Answer 1

You know that for any KVL loop, the sum of all the voltage drops across all resistances will be equal to each other (both equal to the unknown source voltage). Let the internal source resistance be Rs. Then the KVL for the first circuit is:

`V = 0.8 R_(s) +0.8*2\Omega`

The second loop is

`V = 0.4 R_(s) +0.4*3\Omega`

Set these equal since they both equal V:

`0.8 R_(s) +0.8*2\Omega = 0.4 R_(s) +0.4*3\Omega`


`R_(s)(0.8-0.4)=(1.2-1.6)\Omega`


`R_(s)= (-0.4)/(-0.4) = 1\Omega`