## Midterm Solution Q2B

$c=\lambda v$

Hailey Kim 4G
Posts: 110
Joined: Sat Jul 20, 2019 12:16 am

### Midterm Solution Q2B

Q2B. A beam of light at constant intensity and increasing frequency is shown on a metal surface. A detector reads the number of electrons ejected from the sheet of metal. The graph below has a frequency of the incoming light on the X axis and the number of the ejected electrons on the Y axis. Draw the expected plot for the number of the electrons as a function of frequency. Write on the X axis the frequency at which electrons will start to be ejected.

Can someone please explain how to go about this problem and explain why the frequency at which the electrons will start to be ejected is 1.23x10^15 Hz?

kevinchang_4I
Posts: 55
Joined: Tue Nov 13, 2018 12:17 am

### Re: Midterm Solution Q2B

The electrons begin to be ejected at 1.23 x 10^15 Hz because at this point the energy of the incoming photon is enough to overcome the threshold energy of the gold surface. Remember:

Ephoton = Ethreshold + Eemitted electron

ishaa Diwakar 4E
Posts: 56
Joined: Wed Sep 11, 2019 12:17 am

### Re: Midterm Solution Q2B

Also, once the light passes the threshold energy, it can eject electrons. Since the energy of the light is directly correlated to its frequency, increasing the frequency will only cause the energy of the emitted electron to increase. Therefore, the graph you draw should show a horizontal line (at any point of # of electrons) after the calculated frequency.