# Homework Help: Need help with these last few problems

1. Apr 21, 2004

### Spectre32

Alright i scaned in my HW but it didn;t work soo all of my work is not there. Anyways, I need some help with #22 and #23. For 22 i started of with Bhors R = n^2/Z(.5929e-10( but i didn't know what to use for n. THen for 23 I used En=- 1^2/4^2(13.8eV) and got -.8625eV i belive all i need to do is convert it to J's/ Also 21 and 24 i need to g3et get but i'm super lost on those.

Thanks for any help

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2. Apr 22, 2004

Wow, I had that exact same problem on one of my QM tests...

$$r_n = \frac{n^2}{Z} \frac{m_e}{\mu} a_0$$
and
$$E_n = -\frac{Z^2}{n^2}\frac{\mu}{m_e} E_0$$

Make sure to calculate $\mu$ correctly. And you're looking for the first state in 22, so n = 1.

21. Calculate the work required to elevate them to the n = 5 level. Then just use the kinetic energy formula.

24.
$$T = \frac{p^2}{2m}$$