## Post Module #34

$\lambda=\frac{h}{p}$

Mariane Sanchez 1E
Posts: 57
Joined: Fri Sep 29, 2017 7:07 am

### Post Module #34

Hey all,

I figured out the first part of the question, but I'm having troubles finding what makes the speed a reasonable amount.

34. If an electron (mass 9.11 x 10-31 kg) has an associated wavelength of 7.28 x 10-9 m, what is its speed? Is your answer reasonable, why?

A. 1.00 x 10-5 m.s-1. Yes. 1.00 x 10-5 m.s-1 is reasonable for e- as it is less than the speed of light, c = 3.0 x 108m.s-1.

B.1.00 x 10-5 m.s-1. No. 1.00 x 10-5 m.s-1 is not reasonable for e- as it is significantly slower than the speed of light, c = 3.0 x 108 m.s-1.

C. 1.00 x 105 m.s-1 . Yes. 1.00 x 105 m.s-1 is reasonable for e- as it is less than the speed of light, c = 3.0 x 108m.s-1.

D. 1.00 x 105 m.s-1. No. 1.00 x 105 m.s-1 is not reasonable for e- as it is significantly slower than the speed of light, c = 3.0 x 108 m.s-1.

Ryan Sydney Beyer 2B
Posts: 82
Joined: Fri Sep 29, 2017 7:07 am
Been upvoted: 1 time

### Re: Post Module #34

Well for this problem right off the bat I believe the correct answer is C. We can obtain the first value by manipulating the de broglie equation and solving for speed like so :: $v = \frac{h}{\lambda m}$

Now to figure out what makes this a reasonable speed ... Dr. Lavelle told us in lecture today that nothing can travel faster than the speed of light so we know that any value that we obtain as our answer has to be less than the speed of light in order for our answer to make sense physically. Now we know that our answer of 1.00*10^5 m/s is definitely less than 3.00*10^8 m/s so we can say that it is a reasonable speed for an electron because of this reason.