alleryStart learning →A car's starter motor draws 150 A while the battery holds 11.0 V across it. What is the motor's effective resistance?
A0.73 ohm
B13.6 ohm
C0.073 ohm
D1.36 ohm
Answer & Solution
Correct answer: C. 0.073 ohm
1. Rearranging Ohm's law I = V/R gives R = V/I.
2. Substitute: R = 11.0 V / 150 A.
3. Divide: R = 0.073 ohm.
4. A starter has to pass a very large current from a small voltage, so its resistance must be tiny.
5. 13.6 ohm is the trap of dividing current by voltage upside down and misplacing the decimal; it would allow less than one ampere to flow.
_Source: OpenStax College Physics (CC BY 4.0), Ch 20 "Electric Current, Resistance, and Ohm's Law", section 20.2 Ohm's Law: Resistance and Simple Circuits_
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