De Broglie Wavelength?

sharpielife

I'm reviewing for one of my final exam and I can't seem to figure out this problem:

Find the Debroglie wavelength of an electron with a KE of 40 ev.

I got an answer of 3.9 x 10^-10 m.

I keep getting it wrong and I'm not sure what to do.
Thanks in advance!

haruspex

According to http://hyperphysics.phy-astr.gsu.edu...m/debrog2.html you should get half that. If that's right, check oiut the equations there.

Raziel2701

You should only be using two formulas. One involves KE in terms of momentum and mass, and the other relates momentum and wavelength. Your answer is off by a factor of 1/2 so I'm guessing that you are making some mistake in your math.

So why don't you show us what you've done?

sharpielife

Hmm according to the hyperphysics website, my answer should have been
1.85079 x 10 ^ -25

would that be right?
All i did was input the ev value of 40, but I did not input anything for mass or velocity.

Raziel2701

Why don't you show us your work? Your answer is not right yet, you were closer the first time. Mind you that this thread should be at the homework help section.