Sapper

I was walking around my campus the other day and recalled a leacture on electromagnetic field physics. I got to thinking .. as a conductor is moved through a magnetic field (such as the one that the earth produces) an electric potential is created.

The voltage of the induced potential is as follows:

EMF = v* l * B * sin(theta)

EMF = voltage (electromotive force)
v = velocity
l = length of conducting rod
B = magnitude of magnetic field
theta = the angle between the velocity vector and the magnetic field vector

So i thought to myself, how fast would I have to run if I wanted to power my walkman (which runs on 3.0V) if my arm span were 1.8m - assuming of course I were to conduct the electricity from finger tips to my walkman.

Ok, I will now introduce physics land - a place where you can ignore variables to simplify these thought experiments. We will ignore all confounding variables such as resistance, drag, etc.

so we re-arrange the above equation and obtain the following:

v = EMF / l * B * sin(theta)

Ok, how strong is Earth's magnetic field? Well, it is equal to approximately 5.0e-5 T. My velocity will be at 90 degrees to the magnetic field of Earth.

What must my velocity be to power the walkman?

Answter: 33'333 m/s or 33.3 km per second !!

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