De Broglie wavelength of 50 eV electrons and ionisation energy of Fe

[physicsNYC]

Homework Statement

Couple of questions

State the De Broglie Wavelength for electrons with an energy of 50eV

and

the following is a picture is a diagram of the energy levels in Fe: http://www.freeimagehosting.net/image.php?eeddf8b465.jpg
What is the energy required to ionise Fe in in the ground state

Homework Equations

*lambda* = h/p = h/mv = h/sqr(2Em)

The Attempt at a Solution

for the first question i got 1.74x10^-10m but that is not the solution

and for the next question

is it -11.6 or +11.6

 

[rock.freak667]

you mean

$$\lambda = \frac{h}{m \sqrt{2Em}}$$

did you remember to multiply by the mass again in the denominator?

We'd need to see the diagram to help you with the next part of the question.

 

[ideasrule]

If it's "energy required", it's positive; in this case it makes no sense to talk about adding a negative amount of energy.