Question

An automobile starter motor has an equivalent resistance of 0.055 Ï and is supplied by a 12.0 v battery which has a 0.0305 Ï internal resistance. 33% part (a) what is the current to the motor in a?

Answer 1

12 V is the f.e.m.
`\epsilon` of the battery. The potential difference that is applied to the motor is actually the fem minus the voltage drop on the internal resistance r:

`\epsilon - Ir`
this is equal to the voltage drop on the resistance of the motor R:

`RI`
so we can write:

`\epsilon - Ir = RI`
and using
`r=0.0305~\Omega` and
`R=0.055~\Omega` we can find the current I:

`I= (\epsilon)/(R+r)=140~A`