Question Video: Finding the Rest-Mass Energy of an Electron

What is the rest energy of an electron, given its mass is 9.11 ร— 10โปยณยน kg?


Video Transcript

What is the rest energy of an electron, given its mass is 9.11 times 10 to the negative 31st kilograms?

We can call the given electron mass ๐‘š sub ๐‘’, and weโ€™re looking to solve for the electronโ€™s rest energy which we can call ๐‘’ sub zero. To solve for the rest energy, we can recall energy mass equivalence. Summarized by Einsteinโ€™s famous equation, ๐‘’ sub zero, the rest energy, equals ๐‘š sub zero, the rest mass, times ๐‘ squared, where we treat the speed of light ๐‘ as exactly 3.00 times 10 to the eighth meters per second. Since ๐‘ is a constant and ๐‘š sub ๐‘’ is given to us in the problem statement, weโ€™re ready to plug in and solve for ๐‘’ sub zero.

When we do, notice weโ€™ve included an energy conversion factor which will let us give our final answer in units of electron volts rather than joules, a unit that fits more naturally since weโ€™re working with an individual electron. When we calculate ๐‘’ sub zero, we find itโ€™s equal to 0.512 times 10 to the sixth electron volts or 0.512 MeV. Thatโ€™s the rest energy of an electron calculated from its rest mass.

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