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What is the energy of a blue photon with a wavelength of 400 nm?
Wiki User
∙ 13y ago
Energy per photon = ( h ) times (frequency)
( h = Planck's Konstant = 6.63 x 10-34 joule-second )
Frequency = speed/wavelength
Energy = ( h ) x (speed/wavelength) = (6.63 x 10-34) x (3 x 108/4.6 x 10-7) = 4.32 x 10-19 joule
Wiki User
∙ 11y ago
Wiki User
∙ 7y ago4.44 10-19 j
Wiki User
∙ 13y ago400 nm= 400 × 10-9 m
C= λv
3.00 x 108 m/s= 400 × 10-9 m (v)
v= 7.50 × 1014 Hz
E=hv
E= 6.626 × 10-34 J (sec) × (7.50 × 1014 1/sec)
E= 4.97 × 10-19 J
The math above follows you through the steps of finding the energy (in Joules) from a specified wavelength. In this situation, it's best to convert to meters to accommodate the speed of light measured in meters per second further down. (Of course, it's at the physicists discretion to change the units of the speed of light instead). Then you go through a two-step process: Finding the frequency (v) and using the frequency to find the energy (E). To find the frequency, use the formula C= λv where C = the speed of light and λ (lambda) = the wavelength. We know two of the variables (speed of light and wavelength), so we're ready to find the third variable, frequency, which simple arithmetic should provide for you.
Then, knowing the frequency, we can enter the value into the second equation, E=hv, where E = energy (what we're finding) and h = Plank's constant (it may or may not be necessary to know what this represents depending on the level of your course). Again, we plug in the frequency and the constant to find E, energy.
Also, a photon with a wavelength of 400 nm will have an energy of 3.1 eV. (This might actually be called the work function associated with that wavelength.) And its more purple or violet than blue, by the way. To convert wavelength to energy (work function) for a given wavelength, divide 1240 by the wavelength in nm to discover the answer.
See related link below for a corroboration from Wolfram|Alfa.
Wiki User
∙ 13y agoThe answer is 4.4 x 10-19 J, or 2.75 eV.
Here's how I got that number:
The energy of a photon is given by the following equation, E = hf, where E is energy, h is Planck's constant, and f is the frequency of the photon.
Additionally, the speed of a photon of light is given by the following equation, c = fλ, where c is the speed of the photon, which is constant in a vacuum, and λ is the wavelength of the photon.
Therefore, f = c/λ.
Substituting this expression for f into the equation E = hf, gives us the equation E = hc/λ.
Now, as I said before, c is a constant, but so is h. Their values are 3.0 X 108 m/s and 6.63 x 10-34 Js, respectively. Thus, plugging in the value in question for λ, 452 nm, or 452 x 10-9 m, we get:
6.63 x 10-34 Js * 3.0 x 108 m/s / 452 x 10-9 m, which equals
4.4 x 10-19 J, or 2.75 eV.
Wiki User
∙ 13y ago450 nm= 450 × 10-9 m
C= λv
3.00 × 108 m/s= 450 × 10-9 m (v)
v= 6.67 × 1014 Hz
E=hv
E= 6.626 × 10-34 J (sec) × (6.67 × 1014 1/sec)
E= 4.42 × 10-19 J
Wiki User
∙ 14y agoEh, this is really simple, open your book. E=hf=hc/lambda.
Wiki User
∙ 9y agoUse the formula: energy = hc / lambda, where "h" is Planck's constant, "c" is the speed of light, and "lambda" is the wavelength. Don't forget to convert the wavelength to meters first.
Andrew Lopez
(1 eV / 1.6 x 10^(-19))(3.6 x 10^(-19) = 2.25 eV
Wiki User
∙ 14y ago3.6 x 10-19 J
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