## help on the question from Fridays lecture [ENDORSED]

$c=\lambda v$

Alondra Juarez section 1E
Posts: 47
Joined: Fri Sep 29, 2017 7:03 am

### help on the question from Fridays lecture

If 3.61 X 10^-14 j is required to remove an electron with zero kinetic energy from a metal surface, what would be the longest wavelength light that could do this? I am aware we are to rearrange the equation and get hc/E but I'm not to sure what he did after that I don't understand how he got the final answer of 551nm, can someone help me through it?

SammiOrsini_1B
Posts: 45
Joined: Fri Apr 06, 2018 11:04 am

### Re: help on the question from Fridays lecture

In class I saw that Professor Lavelle kept during to the model which showed the light(energy of a photon) hits the metal to remove electrons. The equation is given as energy of photon-energy to remove electrons=energy in excess. Since the energy of a photon is given as E=h*v and c=lamda*v we can rearrange the equations and combine them to get E=h*c/lamda. When we plug in the values and constants we see that we get 551 nm. Im sorry if i am not much help i am still trying to figure things out myself.

Elena 1H
Posts: 27
Joined: Fri Apr 06, 2018 11:04 am
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### Re: help on the question from Fridays lecture  [ENDORSED]

He just plugged in the values. h and c are constants (planck's constant and the speed of light) and they will always be given to us. E is the value given in the problem (3.61 x 10^-14 J). by solving the equation (lambda=hc/E) you get the answer in meters which he then converted to nano meters.