College Physics : Faraday's Law of Induction

Study concepts, example questions & explanations for College Physics

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Example Questions

Example Question #1 : Electromagnetics

A single string of wire has a resistance of \(\displaystyle 10\Omega\). If the wire is connected to a \(\displaystyle 120V\) power source, what is the strength of the magnetic field \(\displaystyle 10cm\) away from the wire?

\(\displaystyle \mu_o=4\pi \times 10^{-7}\frac{T\cdot m}{A}\)

Possible Answers:

\(\displaystyle 100T\)

\(\displaystyle 2.4\times 10^{-5}T\)

\(\displaystyle 2.0\times 10^{-6}T\)

\(\displaystyle 2.4\times 10^{-7}T\)

\(\displaystyle 7.6\times 10^{-5}T\)

Correct answer:

\(\displaystyle 2.4\times 10^{-5}T\)

Explanation:

So this is all about the magnetic field strength around a current carrying wire.

The equation for this is:

\(\displaystyle B = \frac{\mu _{0}I}{2\Pi r}\)

But you must use Ohm's Law \(\displaystyle (V= IR)\) in order to find the current in the wire.

Since the wire has \(\displaystyle 10\Omega\) of resistance and the voltage through the wire is \(\displaystyle 120V\), that means the current in the wire is \(\displaystyle 12A\).

Being sure to change \(\displaystyle 10 cm\) into \(\displaystyle 0.1m\), plug everything in and get the answer, which is

\(\displaystyle 2.4\times 10^{-5}T\)

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