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Question
What is the kinetic energy of an electron in electron volts with mass equal to double its rest mass?
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Solution
If m0 is the rest mass of an electron and c is the speed of light, then kinetic energy (E) of the electron = mc2 − m0c2. ...........(1)
According to the question,
m = 2m0
E = (2m0 − m0)c2
E= m0c2 = 9.1 × 10−31 × 9 × 1016 J
\[E = \frac{9 . 1 \times 9}{1 . 6} \times \frac{{10}^{- 15}}{{10}^{- 19}} = 51 . 18 \times {10}^4 eV = 511\text{ keV}\]
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