- #1
Bindle
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First of all, Hi we haven't even learned the E = ((hc)/λ) in the physics class but we have this question on our test-exam and I hope that it's fairly easy:
A metal plate is shone upon with a monochromatic light. When the wave-length is 550 nm a photo-electric effect is observed where the fastest photo electrons have the energy of 0.45 eV. When the light have 410 nm wave-length the quickest photo electrons get the energy 1.26 eV. Decide the Planck constant with help of these values.
First λ = 550 x 10^9 m
First E = 0.45 eV
Second λ = 410 x 10^9 m
Second E = 1.26 eV
E = h*v
λν = c
Ok, so I start out with, I'm not sure if I even is to use the conversion of eV to J so I can find the constant but it's the only way I can see that we can do this:
0.45 x (1.60217657 × 10^-19) = E
c/λ= v
(3*10^8)/(550 x 10^9) = v
E/v = h
(0.45 x (1.60217657 × 10^-19))/((3*10^8)/(550 x 10^9)) = h
1.3217957e-16 Js = h
Which doesn't look right. But I guess this has to do with photoelectric effect which haven't learned anything about yet, and that I should use the two values and wavelengths in co-operation in some form to get the Plancks constant.
Anybody who could make me see what to do?
Bindle
Homework Statement
A metal plate is shone upon with a monochromatic light. When the wave-length is 550 nm a photo-electric effect is observed where the fastest photo electrons have the energy of 0.45 eV. When the light have 410 nm wave-length the quickest photo electrons get the energy 1.26 eV. Decide the Planck constant with help of these values.
First λ = 550 x 10^9 m
First E = 0.45 eV
Second λ = 410 x 10^9 m
Second E = 1.26 eV
Homework Equations
E = h*v
λν = c
The Attempt at a Solution
Ok, so I start out with, I'm not sure if I even is to use the conversion of eV to J so I can find the constant but it's the only way I can see that we can do this:
0.45 x (1.60217657 × 10^-19) = E
c/λ= v
(3*10^8)/(550 x 10^9) = v
E/v = h
(0.45 x (1.60217657 × 10^-19))/((3*10^8)/(550 x 10^9)) = h
1.3217957e-16 Js = h
Which doesn't look right. But I guess this has to do with photoelectric effect which haven't learned anything about yet, and that I should use the two values and wavelengths in co-operation in some form to get the Plancks constant.
Anybody who could make me see what to do?
Bindle