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Question
What is the kinetic energy of an electron in electron volts with mass equal to double its rest mass?
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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