Hey, I know this is exteremely basic problem and the answer is "easy", but I can't
just get the exact idea why it's so.
"The starting motor of particular car has a resistance of 0,15 Ω and is powered by 12 V battery through a cable which has a resistance of 30 mΩ .
a) What current flows in the starting motor when the voltage is applied?
b) The owner of the vechile finds that it fails to start even after he has replaced the battery. He measures the potential difference across the motor when the current to it is switched on and he finds that this is 11.4 V. Should he replace the motor or check the cable connections?
V = RI
The Attempt at a Solution
a) I just calculated the full resistance and then got current I = 66,7 A.
b) Now here I'm not sure anymore. I know potential difference across any component is V = RI. And I know that if the cables didn't have resistance the potential difference across the motor should be equal to the 12 V.
I think the potential difference as "how much" the components between the two points use the "energy" that battery or emf provides.
Now the motor uses 11.4 V but how I know how much it should be using if it was working properly? I might have lack of understanding about the potential difference also.
Right answer is that he should replace the motor.