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+--- Thread: Light and Kinetic Energy (/showthread.php?tid=40937)
Light and Kinetic Energy - Haseo - 2011-04-23
Okay, so I was wondering; does light possess kinetic energy? If so, how much kinetic energy does it possess per photon such that we aren't buffeted every time we go out in the sun? I don't know if I should be putting this here but I was curious, and it seemed to fit this forum best.
Light and Kinetic Energy - Lozmaster - 2011-04-23
Yes they do.
Photons of light have energy E=pc, where p is the momentum and classically, p= mc (so it also fufils E=mc^2).
However, since light is effectively massless, and yet has a momentum, there must be another expression for momentum.
p = h/wavelength of light.
h = planks constant, 6.63*10^-34
Since we can see wavelengths of light from 400 to 750 nm, energy is higher at lower wavelengths, so for 400nm
E= 6.63*10^(-34)*3*10^8 /(400*10^(-9))= 5*10^(-19) J per photon.
So yeah, not much energy from one photon. Of course, there are photons outside of wavelengths we can see, but any wavelengths significantly shorter than 400nm are blocked by the earths atmosphere anyway.
Light and Kinetic Energy - Haseo - 2011-04-23
Oh, I see. So basically we are buffeted, but to such an infinitesimal degree that we don't notice it?
Light and Kinetic Energy - Hanabira.Kage - 2011-04-23
Haseo Wrote:Oh, I see. So basically we are buffeted, but to such an infinitesimal degree that we don't notice it?
Yeah. The atmosphere probably exerts a greater force on us than photons do. =.=
Light and Kinetic Energy - Shidoshi - 2011-04-23
Not to mention that kinetic energy is not necessarily transferred as translational energy. It can become vibration energy, excite some electrons etc. which wouldn't really make you fall to the side from recieving a flash of light.