## Question from module

Isabel Day 1D
Posts: 48
Joined: Fri Aug 09, 2019 12:15 am

### Question from module

If a problem gives me only the velocity of the ejected electron and the work function for the metal, how do I find the kinetic energy? I can't figure out how to do it without needing the mass of the electron or the frequency of the incoming photon.

This is the problem:
Light hits a sodium metal surface and the velocity of the ejected electron is 6.61 x 105 m.s-1. The work function for sodium is 150.6 kJ.mol-1.

It asks for the kinetic energy of the ejected electron.

Timmy Nguyen Dis 1I
Posts: 107
Joined: Sat Aug 17, 2019 12:17 am

### Re: Question from module

You could just use the mass of the electron, since it's going to be one of those numbers that are given on exams.

Maya Gollamudi 1G
Posts: 100
Joined: Thu Jul 25, 2019 12:15 am

### Re: Question from module

The kinetic energy of an electron is its mass x velocity. You can use the mass of an electron to find the KE, which is 9.11 x 10^-31 kg (the mass of an electron will be given to us on tests).

Ashley R 1A
Posts: 41
Joined: Sat Aug 24, 2019 12:16 am

### Re: Question from module

You're going to use the equation E = 1/2 m v^2. In this case, E stands for the kinetic energy of an electron. The mass of an electron will always be constant at 9.109x10^-31 kg, it's on the formula sheet that we're given on tests.

quresh3E
Posts: 36
Joined: Wed Sep 18, 2019 12:17 am

### Re: Question from module

I worked backwards and solved for the wavelength then inputted it into the E=H*C/v equation. Why is this wrong?

Ian Morris 3C
Posts: 101
Joined: Wed Sep 18, 2019 12:18 am

### Re: Question from module

Timmy Nguyen Dis 3F wrote:You could just use the mass of the electron, since it's going to be one of those numbers that are given on exams.

Is the mass of an electron on the reference sheet?