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### Example from Friday's Lecture (10/12/18)

Posted: Sun Oct 14, 2018 5:00 pm
Hi,

On Friday we went over a problem at the end of class that asked if the wavelength of an electron traveling at 5.3 x 10^6 m/s could be calculated. When we plugged in the numbers, we were given 9.11 x 10^-31 kg. Where does this number come from?

Thank you!!

### Re: Example from Friday's Lecture (10/12/18)

Posted: Sun Oct 14, 2018 5:04 pm
9.11 * 10^-31 kg is the weight of an electron. This value is given

### Re: Example from Friday's Lecture (10/12/18)

Posted: Sun Oct 14, 2018 5:14 pm
You use the mass of the electron when calculating the momentum (p) in the problem. I believe the example he gave us listed the velocity of the electron but not the mass of it. So to calculate p=(m)(v) he plugged in the mass which I guess is considered a constant.

### Re: Example from Friday's Lecture (10/12/18)

Posted: Sun Oct 14, 2018 5:58 pm
Yes, Lavelle said that the mass is given. So it is safe to assume that the mass will be on the constants sheet for any tests/exams.