Practice Problem 1B.15

[Diego Salgues 2K]

Hello,

I'm having trouble with 1B.15. Specifically, I don't know how to do part (c)...

The velocity of an electron that is emitted from a metallic surface by a photon is 3.6 x 10^3 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 2.5 x 10^16 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?

If anyone could provide help, it'd be greatly appreciated.

Thank you,

D

[Adele Nguyen 2G]

(a) Use De Broglie's formula to solve for wavelength.
(b) Using the threshold frequency given, multiply by Planck's constant to get the work function.
(c) Solve for the kinetic energy (1/2 x mass of electron x velocity squared). We now know both the kinetic energy and the work function (from b). Add them together to get the energy of the incoming light (radiation that caused photoejection of the electron). Using E = h(c/lambda), solve for the wavelength (lambda).
(d) From the wavelength, you can refer to the electromagnetic spectrum to determine the kind of radiation that was used.