Question

What is the rest energy of an electron, given its mass is $9.11 \times 10^{-31} \textrm{ kg}? Give your answer in joules and MeV.

$8.19 \times 10^{-14} \textrm{ J}$

$511 \textrm{ keV}$

$511 \textrm{ keV}$

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This is College Physics Answers with Shaun Dychko. The rest energy of an electron is its mass times <i>c</i> squared. That's 9.11 times 10 to the minus 31 kilograms times 2.998 times 10 to the 8 meters per second squared giving 8.19 times 10 to the minus 14 joules. We can express that energy in electron volts by multiplying the joules by 1 electron volt for every 1.602 times 10 to the minus 19 joules and the joules cancel giving us 511 kiloelectron volts, is another way to express that same energy.