Question:
Help with energy question please? I'm just not sure which formula to use.?
Lily A
2011-06-02 16:50:50 UTC
A photon is traveling. Its wavelength is 5.3 x 10^-7 meters. What's the energy?
If you give me a formula I could probably figure it out, I'm just not sure which one to use.
Five answers:
wolf_235813
2011-06-02 17:37:55 UTC
E = hf



where



E = energy (J)

h = Planck's constant = 6.626 x 10^-34 J s

f = frequency (Hz)





In addition, frequency and wavelength are related:



f = c / λ



where



f = frequency (Hz)

c = the speed of light = 2 x 10^8 m / s

λ = wavelength (m)





Therefore:



E = h c / λ



E = (6.626 x 10^-34 J s)(3 x 10^8 m / s) / (5.3 x 10^-7 m)



E = 3.75 x 10^-19 J





Hope this helps...good luck!
oldprof
2011-06-03 00:28:04 UTC
Tsk tsk. One doesn't learn physics by memorizing formulas. What you should be learning here is the physics, not the formulas. So what's the physics?



Simple... I mean it... simple. It's this.



Photonic energy is proportional to the frequency of the photon. That's it. That's all there is. Now knowing the physics you can write:



E ~ f, where E is energy and f is frequency. The ~ means "is proportional to."



Where there is a proportional relationship, there must be a constant of proportionality. In this case, h, Plank's Constant, is that constant of proportionality to make the proportional relationship (with the ~) into an actual equation (with a =). So E ~ f becomes E = hf and there's your first equation, which we derived from the physics.



But this is about frequency, not wavelength, which is the given. So more physics here.



For electro magnetic fields the speed of the photons is fixed at C, the speed of light in a vacuum. So if the distance a photon travels is its own wavelength, L, we can write distance = speed X time traveled = CT = L; where T = 1/f is the time to travel one wavelength and we call that the period.



So now we have E = hf = hC/L because C/L = 1/T = f from CT = L.



And there you are. By knowing the physics, we derived E = hC/L; where you can look up h and C, and L = 5.3E-7 m is given. E will be in Joules when h and C are in kms SI units consistent with the wavelength in meters.
?
2011-06-02 23:59:32 UTC
Hey use E=hf. Find f (frequency ) using the v=f >< wavelength. (3.0 >< 10^8 = f >< wavelength). Goodluk.
anonymous
2011-06-03 00:00:18 UTC
E = hf



Energy of Photon = Planks constant x Frequency of photon



(Planks constant is 6.626x10^-34)
ßąЯΥסИŠ
2011-06-03 00:19:54 UTC
you should first calculate the frequency

frequency = speed of light ÷ wavelength



then you get the energy from:

Energy = Planck's constant × Frequency


This content was originally posted on Y! Answers, a Q&A website that shut down in 2021.
Loading...