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I had to find the kinetic energy of electron with wavelength $2$ pm. I used the formula $$ KE = \frac{p^2}{2m} = \frac{h^2}{\lambda^2 2m}$$

which gave me result, $KE = 376.9$ KeV. But the answer given in the book is $292$ KeV. Am I making a mistake in calculating it?

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closed as too localized by David Z Jan 2 '12 at 8:35

This question is unlikely to help any future visitors; it is only relevant to a small geographic area, a specific moment in time, or an extraordinarily narrow situation that is not generally applicable to the worldwide audience of the internet. For help making this question more broadly applicable, visit the help center.If this question can be reworded to fit the rules in the help center, please edit the question.

Hi orion - In general, if there's some conceptual issue that you think is causing you to get the wrong answer, you can ask about that, but this site is not meant to be a place to check your work. (That being said, I get the same result as you...) – David Z Jan 2 '12 at 8:36
I get 292.9keV. Note that this is relativistic case. – Adam Zalcman Jan 2 '12 at 8:48
@ Adam Zalcman: Thanks. Can you tell me how did you knew that this is relativistic case? Sorry for the ignorance, but I really don't know how to know from the wavelength that an electron is relativistic or not? Please guide me. – orion Jan 2 '12 at 8:52
The kinetic energy you got using non-relativistic formula was of the same order of magnitude as electron's rest energy (511keV). If that happens, it is worth calculating both and checking how much they agree. – Adam Zalcman Jan 2 '12 at 8:57
@ Adam Zalcman: Thanks for this important point. – orion Jan 2 '12 at 9:14