[neverworks]

Hi,

I had a query about a problem from my Physical Chemistry textbook.

To what speed must an electron be accelerated for it to have a wavelength of 3cm?

So, I am using the equation v = λm / h

m = 9.1 x 10^-31 kg
λ = 3 x 10^-2 m
h = 6.63 x 10^-34 Js

This gives me the answer 41m/s which, to me, seems a little slow for an electron!

Can anyone offer any guidance on where I may be going wrong?

Sean

[Corribus]

So, I am using the equation v = λm / h

Well, this is most of your problem. Your equation is wrong.
BUT, you should be expecting a very small velocity. Instead of thinking of it this way, you should be thinking that a wavelength of 3 cm is really long for an electron. An electron has to go really slow to have a wavelength so BIG.

[Enthalpy]

Hints:

Wavelengths and wave vectors relate simply with the momentum, which is m*V at low speed.

Electrons define the size of atoms, where their energy is (minus) a few eV. Since 3cm is MUCH bigger than an atom, the electron's energy and speed must be small.