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## Homework Statement

**Light with a wavelength of 630nm is directed at a metallic surface that has a work function of 1.5 eV. Find:**

**a) The maximum kinetic energy of the emitted electrons.**

b) The cutoff potential required to stop the photoelectrons.

b) The cutoff potential required to stop the photoelectrons.

## Homework Equations

E

_{k}= hc / λ - W

E

_{k}= eV

_{o}

## The Attempt at a Solution

a)

λ = 630nm = 6.3 x10

^{-7}m

W = 1.5eV (1.60x10

^{-19}J/eV)

W = 2.4 x10

^{-19}J

E

_{k}= hc / λ - W

E

_{k}= (6.63 x10

^{-34}J)(3.0 x10

^{8}m/s) / (6.3 x10-7m) - 2.4 x10

^{-19}J

E

_{k}= 7.57 x10

^{-20}J

The maximum kinetic energy is 7.57 x10

^{-20}J.

b)

E

_{k}= eV

_{o}

7.57 x10

^{-20}J = (1.60 x10

^{-19}) V

_{o}

V

_{o}= 7.57 x10

^{-20}J / (1.60 x10

^{-19})

V

_{o}= 0.47 V

The cutoff is 0.47 V.

I am uncertain if my answer to part a) is correct, I have reviewed all my steps and can't find an error, however, for all of the questions I have done so far, the answer has always been x10

^{-19}, whereas my answer here, is 7.57 x10

^{-20}J is x10

^{-20}. Is this an acceptable answer? Is it possible for it to not always be to the

^{-19}J? or did I make an error somewhere in my calculations?