## hw 1B.15 part c

Joanna Mendoza 3J
Posts: 20
Joined: Sat Aug 24, 2019 12:17 am

### hw 1B.15 part c

Problem: The velocity of an electron that is emitted from a metallic surface by a photon is 3.6 x 10^3 km.s^-1. (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 2.50 3 1016 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 was able to solve parts a and b but what equation would I use to be able to solve c? Can somebody show me the steps and explain to me why they are done?

Andrew Jang 4D
Posts: 50
Joined: Sat Aug 17, 2019 12:18 am

### Re: hw 1B.15 part c

You should find the energy of the photon that caused the electron to eject as well as move at 3.6*10^3 km/s. You already found the energy required to eject the electron from the metal surface in part B, so all you need now is the kinetic energy of the electron that makes it move at its speed. You can use (1/2)mv^2 to find it. Once you add that to your answer from part B, you get the total energy of the photon. From there, you can use E=hv and c=λv to find the wavelength λ.

Joanna Mendoza 3J
Posts: 20
Joined: Sat Aug 24, 2019 12:17 am

### Re: hw 1B.15 part c

Thank you for explaining that clearly!
For part d, how would I determine the kind of electromagnetic radiation that was used?

Jesalynne 2F
Posts: 100
Joined: Wed Sep 18, 2019 12:18 am

### Re: hw 1B.15 part c

I think you would use the wavelength you got from part c and find where it is on the electromagnetic spectrum. There is a figure and table in 1A.2 Electromagnetic Radiation that you can refer to.