De Broglie wavelength and kinetic energy of electrons at 1.0 eV, 100 eV, and 650 nm

[SGL18]

Homework Statement

What is the DeBroglie wavelength of an electron whose energy is (a) 1.0eV (b) 100eV?
What is the kinetic energy in eV of an electron whose DeBroglie wavelength is that of visible red light at 650nm?

Homework Equations

λ=h/p = h/mv h = Planck's constant mv = particle

The Attempt at a Solution

 

[Sebastian]

Well, what have you tried? Where did you get stuck?

 

[SGL18]

i used the formula λ=h/(Em)^1/2 and correctly got 1eV to equal 1.23x10^-9.
For 100eV would i just multiply 100 by 1.6x10^-19? then plug it back into the equation?

 

[Redbelly98]

That should work.

Did you really mean to use p=(Em)^1/2 or is that a typo -- there is a missing number in the expression?