## Photoelectric Effect Post-Module Assessment #33

$c=\lambda v$

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Joined: Wed Sep 30, 2020 9:35 pm

### Photoelectric Effect Post-Module Assessment #33

Hi! Can anyone help me with this question?

Molybdenum metal must absorb radiation with a minimum frequency of 1.09 x 1015 s-1 before it can emit an electron from its surface.
What is the minimum energy needed to produce this effect?

reyvalui_3g
Posts: 85
Joined: Wed Sep 30, 2020 9:52 pm

### Re: Photoelectric Effect Post-Module Assessment #33

In order to calculate the minimum energy needed to remove the e- from the surface of the metal we can use the equation:

Energy = (Frequency)(h)

We know already that h (Planck's Constant) is : 6.626 x 10^-34 J.s.

Furthermore, the problem gave us the frequency 1.09 x 10^15 s-1. Now all that has to be done is to multiple the two numbers and get the energy value.

305572629
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Joined: Wed Sep 30, 2020 9:41 pm

### Re: Photoelectric Effect Post-Module Assessment #33

Does anyone know how to know whether to use use the Ephoton equation versus the other energy/wavelength equations?

BrittneyMyint1D
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### Re: Photoelectric Effect Post-Module Assessment #33

305572629 wrote:Does anyone know how to know whether to use use the Ephoton equation versus the other energy/wavelength equations?

Hi, I would say it depends on the given information. I would try to figure out the knowns and unknowns, and then looking at the available equations, you could find which equations you need to use to get to the desired answer.
For example, when the question gives us information about the Ephoton and kinetic energy, and they want us to find how much energy was needed to eject an electron, we could assume that we use the Ephoton equation to find the threshold energy.
If the question asks for wavelength/frequency, we would use the other equations such as E=hv. There's also some examples in his audio-visual topic regarding the photoelectric effect.

Hope that makes sense!