## DeBroglie Equation Post Assessment

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

gabbym
Posts: 76
Joined: Wed Apr 11, 2018 3:00 am

### DeBroglie Equation Post Assessment

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?
Can someone help me with this problem? I think I am rearranging the equation wrong or something. I thought it should be v=h/m*wavelength, but I keep getting the wrong answer.

yaosamantha4F
Posts: 31
Joined: Fri Sep 28, 2018 12:29 am

### Re: DeBroglie Equation Post Assessment

That should be correct, although when you're plugging numbers into your calculator, make sure to put parentheses around (m*wavelength). It is not reasonable for an electron to be faster than the speed of light, but if the electron is below 10^5m/s, this may also be too slow to be reasonable.

Grace Kim 1J
Posts: 60
Joined: Fri Sep 28, 2018 12:18 am
Been upvoted: 1 time

### Re: DeBroglie Equation Post Assessment

Your formula is correct; After you rearrange the DeBroglie Equation to set it equal to the velocity, you get v = h/(wavelength) (mass). When you plug in the numbers into the equation, you should get 1.00 m.s^-1 as the answer.
It might be a simple calculation error!

h= 6.62608 x 10^-34 J.s
wavelength= 5.3 x 10^6 m
mass= 9.11 x 10^-31 kg

404536963
Posts: 29
Joined: Fri Feb 02, 2018 3:02 am

### Re: DeBroglie Equation Post Assessment

The answers above give you the correct answer, but just make sure that you use parenthesis in your calculator! I know that in my experience I sometimes get the wrong answer when I'm dividing by something like Planck's Constant, it can get confusing if you are dividing while multiplying by 10^34, so just make sure you're doing it in steps!

904983525
Posts: 17
Joined: Fri Sep 28, 2018 12:26 am

### Re: DeBroglie Equation Post Assessment

404536963 wrote:The answers above give you the correct answer, but just make sure that you use parenthesis in your calculator! I know that in my experience I sometimes get the wrong answer when I'm dividing by something like Planck's Constant, it can get confusing if you are dividing while multiplying by 10^34, so just make sure you're doing it in steps!

Thank you for this, I was having a problem too with my calculation.