Finding wavelength from a given velocity of an electron

Camille Marangi 2E
Posts: 60
Joined: Fri Sep 28, 2018 12:26 am

Finding wavelength from a given velocity of an electron

Hi so I am currently stuck on the HW question 1B.15 which is as follows:

The velocity of an electron that is emitted from a metallic surface by a photon is 3.6x10^3 km/s
(a) What is the wavelength of the ejected electron?
(b) No electrons are emitted from the surface of the metal until the frequency of the radiation reaches 2.50x10^16 Hz. How much energy is required to remove the electron from the metal surface?
(c) What is the wavelength of the radiation that caused photoejection of the electron?
(d) What kind of electromagnetic radiation was used?

I get that you find the kinetic energy using KE=1/2(mass of electron)(velocity of electron)^2 for which I get KE=1.6396x10^-24 but from there I have no idea what to do. Any help is appreciated!

pauline_le_3I
Posts: 21
Joined: Fri Sep 28, 2018 12:25 am

Re: Finding wavelength from a given velocity of an electron

I'm not completely sure about the rest of the questions, but for a) The KE is measured in Joules, so you can plug what you found into the equation:
$E=\frac{ch}{\lambda }$

to find the wavelength, where E is what you found and c (speed of light) and h (Planck's constant) are given.

pauline_le_3I
Posts: 21
Joined: Fri Sep 28, 2018 12:25 am

Re: Finding wavelength from a given velocity of an electron

I also found this post that has part c worked out, so if you want to look at this one as well!

viewtopic.php?f=16&t=33344&p=107986&hilit=The+velocity+of+an+electron+that+is+emitted+from&sid=503b67247442334fd29256ccbb4dc65f#p107986