I need help answering this problem:
The work function for chromium metal is 4.37 eV. What wavelength of radiation must be used to eject electrons with a velocity of 1.5x10^3 km/s?
Week 3 discussion, question 6 [ENDORSED]
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Re: Week 3 discussion, question 6
This is a photoelectric problem so use the photoelectric equation we have learned. Also the work function of the metal is 4.37eV. You need to convert to J. 1eV = 1.60 * 10^-19 J.
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Re: Week 3 discussion, question 6 [ENDORSED]
First, you have convert 4.37 eV to J so you have 4.37 eV x [(1.602 x 10^-19 J)/1 eV] = 7.0 x 10^-19 J. It also tells you that this is your work function so this is your 
You should also convert v = 1.5 x 10^3 km/s to 1.5 x 10^6 m/s since we will be working with Joules.
Then you use
to find the kinetic energy so KE = (1/2)(9.1095 x 10^-31 kg)[(1.5 x 10^6 m/s)^2]. You end up with KE = 1.0248 x 10^-18 J. The units end up in Joules because 1 J = 1 kg(m^2)(s^-2)
Now that you have the KE and the work function, you can find the energy of the photon by using
so E = (1.0248 x 10^-18 J) + (7 x 10^-19 J) = 1.7248 x 10^-18 J
To find the wavelength, you can then combine the E = hv and c =
v to get the equation /E_{p})
This gives you
= [(6.626 x 10^-34 Js)(3.0 x 10^8)]/(1.7248 x 10^-18 J) = 1.15 x 10^-7 m
Convert to nanometers and you get 115 nm.
(FYI, this is question 1.34 from the textbook)
You should also convert v = 1.5 x 10^3 km/s to 1.5 x 10^6 m/s since we will be working with Joules.
Then you use
Now that you have the KE and the work function, you can find the energy of the photon by using
To find the wavelength, you can then combine the E = hv and c =
This gives you
Convert to nanometers and you get 115 nm.
(FYI, this is question 1.34 from the textbook)
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