Part 07 · Electric fields and potential · Card 8 of 10
Potential difference
Voltage between two points. A charge q moved across a voltage V gains energy qV.
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Analogy
A ski lift raises skiers, a battery raises charges.
Example
Electron in 100 V
W = q VW = 1.6e-19 x 100W = 1.6e-17 J
In practice
An electron accelerated through 100 V gains 1.6e-17 J.
Questions people ask
What is an electron-volt?
An electron-volt is the energy an electron gains going through one volt: 1.6e-19 J. It is a handy unit for atoms and particles, where joules are inconveniently large. A photon of visible light carries around 2 to 3 electron-volts of energy.
How do I find the speed of a charge accelerated through a voltage?
Set the energy gained equal to kinetic energy: qV = 1/2 m v squared. For an electron through 100 V, v = sqrt(2 x 1.6e-19 x 100 / 9.11e-31), which is about 5.9e6 m/s. For high speeds you need relativity.