## Test #2 Question 7 [ENDORSED]

Odalys Cuevas 1C
Posts: 31
Joined: Fri Apr 06, 2018 11:02 am

### Test #2 Question 7

Copper is used widely in electrical wiring due to its high electrical conductivity and malleability. The threshold energy or "work function" of the copper atom is 7.52* 10^-19 J. What is the maximum wavelength of light (lowest energy) you need to shine onto the copper metal in vacuum to eject electrons?

Can someone please help me answer this question. I used the formula E= "work function" + Ek. How do i get the wavelength from there?

Thank you

Heung Ching Chia 1E
Posts: 25
Joined: Mon Apr 09, 2018 1:38 pm

### Re: Test #2 Question 7  [ENDORSED]

The question asks for the max wavelength or lowest energy, meaning when you shine the light on the metal surface, an electron just gets enough energy to be popped out onto the surface of the metal, but there will not be any extra energy for the electron to have kinetic energy. Therefore, you should set Ek=0.

Then, to get the wavelength, E=hc/wavelength, so you just arrange the equation into hc/wavelength=work function ( 7.52* 10^-19 J) +0, where h and c are constants.

Caitlyn Ponce 1L
Posts: 30
Joined: Fri Apr 06, 2018 11:04 am
Been upvoted: 1 time

### Re: Test #2 Question 7

Whenever the maximum wavelength of light is asked for, the kinetic energy of the ejected electrons will equal zero (the incoming light just meets the requirement of the work function).
In this question, the work function is equal to the energy of the incoming light. To get the answer, plug the energy value into the equation, wavelength=hc/E.