photon kinetic energy


by nuby
Tags: energy, kinetic, photon
nuby
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#1
Apr29-08, 02:50 PM
P: 364
How is a photon's energy determine in relation to it's wavelength and frequency?
For example, 20hz vs. 400ghz electromagnetic waves.
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pmb_phy
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#2
Apr29-08, 03:19 PM
P: 2,955
Quote Quote by nuby View Post
How is a photon's energy determine in relation to it's wavelength and frequency?
For example, 20hz vs. 400ghz electromagnetic waves.
The energy of a photon, E (which can be considered as all kinetic energy since the proper energy = E0 = 0 and E = K + E0 = K), is related to the photon's frequency, f, by E = hf where h = Planck's constant = 6.626068 10-34m2kg/s.

Pete
nuby
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#3
Apr29-08, 08:58 PM
P: 364
can E=1/2mv^2 be applied to photons ever?
or E=mc^2

lbrits
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#4
Apr29-08, 11:10 PM
P: 410

photon kinetic energy


The proper relativistic equation is
:[tex]E^2 = p^2c^2 + m^2 c^4[/tex], which works just fine for photons when [tex]m = 0[/tex].

For ordinary particles, one can Taylor expand [tex]E = \sqrt{p^2c^2 + m^2 c^4}[/tex] to get a non-relativistic equation most people use... but for photons, you can't do this, and [tex]E = pc[/tex] simply.

According to de Broglie, [tex]p = h \nu[/tex], of course.
pmb_phy
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#5
Apr30-08, 07:16 PM
P: 2,955
Quote Quote by nuby View Post
can E=1/2mv^2 be applied to photons ever?
or E=mc^2
No.

Pete


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