# Photoelectric effect find velocity?

#### Sara077

1. Homework Statement
Light illuminates a metallic surface with work function of 1.20 eV. It takes 1.0 V of retarding potential to stop all of the photoelectrons from reaching the opposite plate. Find the maximum speed of the photoelectrons.

2. Homework Equations
hf = w

hf = w + Ek

3. The Attempt at a Solution

First work function = 1.20eV(1.60x10-19 J/eV) = 1.92x10-19 J

Not really sure how to do this problem... but giving it a go here:

First,

hf = w

f = w/h

f = 1.92x10-19 J / 6.63x10-34 Js

f = 2.9x1014 Hz

Now i got the frequency, i assume i use:
hf = w+ Ek
Ek = hf - w
1/2mv2 = hf - w

Is this correct so far? If yes do i just plug in the numbers and solve for "v" also not really sure what to do with the retarding potential?

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#### Sara077

Or if the above isnt correct i tried it a different way...

Ek = eV
Ek = (1.60x10-19 C) (1.6V)
Ek = 2.56x10-19 J
^^ Should i subtract the work function from this?

Ek = 1/2mv2
2.56x10-19 J = 1/2 (9.11x10-31 kg (v)2
5.62x1011 Jkg = v2
7.5x105 m/s = v

Is this one correct?? Im just confused

"Photoelectric effect find velocity?"

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