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### College Physics (Urone)

Book edition 1st Edition
Author(s) Paul Peter Urone
Pages 1272 pages
ISBN 9781938168000

# What is the effective resistance of a car’s starter motor when $${\bf{150}}\;{\bf{A}}$$ flows through it as the car battery applies $${\bf{11}}{\bf{.0}}\;{\bf{V}}$$ to the motor?

The effective resistance of the car’s starter motor is $$0.073\;{\rm{\Omega }}$$.

See the step by step solution

## Step 1: Identification of the given data

The given data can be listed below as,

• The value of current flow is, $$I = 150\;{\rm{A}}$$.
• The potential difference of the battery is, $$V = 11.0\;{\rm{V}}$$.

## Step 2: Significance of the Ohm’s law

According to Ohm's law, the value of potential difference across a specific electrical circuit is directly proportional to the electrical current flow. The proportionality constant in this relationship is the circuit element's resistance.

## Step 3: Determination of the effective resistance of the car’s starter motor

The expression to calculate the effective resistance of the car’s starter motor is expressed as,

\begin{align}V = IR\\R = \frac{V}{I}\end{align}

Here, $$R$$ is the effective resistance of the car’s starter motor.

Substitute all the known values in the above equation.

\begin{align}R = \left( {\frac{{11.0\;{\rm{V}}}}{{150\;{\rm{A}}}}} \right)\\ \approx 0.0733\;{\rm{V/A}}\\ \approx \left( {0.0733\;{\rm{V/A}}} \right)\left( {\frac{{1\;{\rm{\Omega }}}}{{1\;{\rm{V/A}}}}} \right)\\ \approx 0.073\;{\rm{\Omega }}\end{align}

Thus, the effective resistance of the car’s starter motor is $$0.073\;{\rm{\Omega }}$$.