## Post Module Question [ENDORSED]

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

SaniShabgahi3N
Posts: 21
Joined: Wed Sep 21, 2016 2:57 pm

### Post Module Question

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?
I continue getting the answer 1.00x10^4 and don't understand what I did wrong. Also, how would I know if the answer is reasonable compared to the speed of light.

Minu Reddy
Posts: 31
Joined: Sat Jul 09, 2016 3:00 am

### Re: Post Module Question  [ENDORSED]

Perhaps, there is an error in your calculations because when you multiply the given wavelength by the mass of the electron you get a value that is 6.63*10^-39. Then when you divide "h" Planck's constant by that value you must get 1*10^5. In regards to if the answer is reasonable, I know that the speed of the electron must be less than the speed of light, but I am not sure to what degree this is applicable. Therefore, I would assume that the answer if d. But, I would really appreciate it if someone could please explain part B of this question in more detail!

Thank you

Alexandra Watts 3L
Posts: 14
Joined: Wed Sep 21, 2016 2:56 pm

### Re: Post Module Question

The speed of the electron can not be faster than the speed of light, therefore if it the speed is a higher number than the speed of light the speed calculated would be unreasonable.

Janice Kim 3I
Posts: 33
Joined: Wed Sep 21, 2016 2:56 pm

### Re: Post Module Question

The speed of light is what we can compare to in terms of velocity. The answer cannot be reasonable if the speed is greater than the actual speed of light. It is similar to the concept of comparison when we are calculating the uncertainty in velocity. If the uncertainty is greater than the speed of light, then we are unable to localize the electron.