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# Stuck! watch

1. Ok so i'm revising the photoelectric effect for AS physics and im struggling with the equations.

The question i need to answer is:

A gold surface is illuminated with monochromatic ultra violet light of frequency 2.10 x 12^15 Hz. The maximum kinetic energy of the emitted photo electron is 6.20 x 10^19 J. Calculate

a) the energy in J of the incident photon
b) the work function of gold

So for a i do E=hf which gives me a total of 1.39 x 10^50 ?? am i way off?

so then i used the photo electric equation hf=Ekmax + phi and i took the max kinetic energy away from hf to leave me with the work function??

Sorry if that makes no sense, any help would be greatly appreciated
2. (Original post by lornielou2012)
Ok so i'm revising the photoelectric effect for AS physics and im struggling with the equations.

The question i need to answer is:

A gold surface is illuminated with monochromatic ultra violet light of frequency 2.10 x 12^15 Hz. The maximum kinetic energy of the emitted photo electron is 6.20 x 10^19 J. Calculate

a) the energy in J of the incident photon
b) the work function of gold

So for a i do E=hf which gives me a total of 1.39 x 10^50 ?? am i way off?

so then i used the photo electric equation hf=Ekmax + phi and i took the max kinetic energy away from hf to leave me with the work function??

Sorry if that makes no sense, any help would be greatly appreciated
that would be a heck of an energetic photon.
You've got the right formula but something has gone wrong in the calculation.
Also 2.10*12^15 is a non standard way of expressing a number, are you sure you copied that right?
3. Thats what I thought!

it should be (6.63 x 10-34) X (2.10 X 1015)

And i've just spotted my mistake! i think the answer should be 1.39x10-18

Have i done the right thing to find the work function?

4. You're right.
Obv it's good skills to be able to spot when an answer is unreasonable and re check your calculation in exams.

Fwiw 10^12 electron volts is a high energy for a 'lab made' particle (if you have a £multi-million accelerator), and an electron volt is of course a far smaller unit than a joule.
5. (Original post by Joinedup)
You're right.
Obv it's good skills to be able to spot when an answer is unreasonable and re check your calculation in exams.

Fwiw 10^12 electron volts is a high energy for a 'lab made' particle (if you have a £multi-million accelerator), and an electron volt is of course a far smaller unit than a joule.
10^12 eV is only a factor of 7 away from the highest energy collisions ever achieved in ANY particle accelerator including the £multi-billion ones!
6. (Original post by uberteknik)
10^12 eV is only a factor of 7 away from the highest energy collisions ever achieved in ANY particle accelerator including the £multi-billion ones!
I can remember that the tevatron was named for being a Tera (10^12) electron volt collider and we're still not an order of magnitude higher.
It'd seem strange if a cheapo uv lamp was making more energetic particles than that.

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