Photoelectrons with a maximum speed of 7.00 · 105 m/s are ejected from a surface in the presence of light with a frequency of 8.00 · 1014Hz. Calculate the energy required to eject photoelectrons from the surface.

Question

anonymous · Answer

@Nali

nali · Answer

do you mean the speed is 7 X 10^5 and frequency is 8 X 10^14 ?

anonymous · Answer

Yes, sorry, it didn't transfer over quite right.

nali · Answer

ok so 1st step is to find the kinetic energy 

KE= 1/2 mass x velocity ^2 = 1/2 mv^2 

so you plug in the given velocity with the mass of the electron which is 9.11x10-31kg

nali · Answer

2nd step is to plug in the kinetic energy in the equation of threshold frequency 

hf= Work + KE 

So h is a constant that equals 6.626 x 10^-34 J-s and the frequency is given 

so you have to find work of ejecting photoelectrons.

nali · Answer

Work is going to be in Joules (J) and that would be your answer

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nali · Answer

@historygeek96 when you get ur final answer just tell me to make sure

nali · Answer

The mass of an electron is supposed to be 9.11x10^-31kg  sorry, I forget to put the carrot there

anonymous · Answer

Thanks, I found the same thing in my lesson

nali · Answer

ok great!

anonymous · Answer

-2.2295x10^-19

anonymous · Answer

Unfortunately my options are 3.1x10^-19 and 7.5x10^19

nali · Answer

ok let me do it, just give me a moment

anonymous · Answer

Okay thank you so much

nali · Answer

ok I think you stopped after finding the KE and you did not continue by doing hf-KE to find the work in ejecting the photoelectrons

nali · Answer

KE=2.23 X 10^-19 but why do you have a negative sign there?

anonymous · Answer

hf is planck's constant right?

nali · Answer

yes

anonymous · Answer

I did continue past finding KE

anonymous · Answer

I keep redoing it and I keep getting the same thing...

anonymous · Answer

Oh I just got 3.074500e-19

anonymous · Answer

Which is one of the options I'm given

nali · Answer

I know wht you did your calculator is in radians mode

anonymous · Answer

Actually, I wasn't using frequency, I thought hf stood for planck's constant, not planck's constant multiplied by the frequency

anonymous · Answer

I thought it was the calculator too but I used two of them and got the same answers.

nali · Answer

oh ok so I know the answer now, what do you have?

anonymous · Answer

It was 3.1x10^-19.

nali · Answer

yes good job that is right

anonymous · Answer

Yeah, its an online class so once I've turned it in its graded instantly.