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# E = hf question

boinsterman
For the equation
 Quote: E = hf

( E = energy, h = Plank's constant, and f = frequency),
where does the extra energy go to or come from at different frequencies, such as when leaving a gravity field? Otherwise, the energy would be created or destroyed, which I understand is impossible.
kelseymh
boinsterman wrote:
For the equation
 Quote: E = hf

( E = energy, h = Plank's constant, and f = frequency),
where does the extra energy go to or come from at different frequencies, such as when leaving a gravity field? Otherwise, the energy would be created or destroyed, which I understand is impossible.

Gravitational redshift can be interpreted as the photons "losing energy" as they climb out of a gravity field, just as a ball slows down when thrown upward.
boinsterman
They lose kinetic energy but gain potential energy, which I understand is interpreted as having negative value? I was wondering if the same is responsible for greater amplitudes, in the same fashion as an orbinting body moving to a higher orbit if it loses energy.
kelseymh
 boinsterman wrote: They lose kinetic energy but gain potential energy, which I understand is interpreted as having negative value? I was wondering if the same is responsible for greater amplitudes, in the same fashion as an orbinting body moving to a higher orbit if it loses energy.

No, there's no change in amplitude. Each photon has an energy of E = hf, and they all have the same amplitude -- one photon. The frequency, and hence energy, changes, but one is one is one

If you choose to measure a high-intensity light source (integrating over all the photons, rather than one at a time), then you could see a drop in intensity at your detector, which will scale like 1/r^2. That's just the trivial spreading of the beam, and assumes that your detector is small (imagine turning on a searchlight on the moon, and looking at it with your eye down here on earth). If your detector is as large as the whole beam at the distance you're measuring, then you won't see any intensity loss.
chatrack
Hi,
I think the effect of gravitational field and change in gravitational potential energy
comes when the mass or masses are very large.

In case of electron the mass is very less so, in the case of of electron(consider it as wave - cathod ray)
the effect of change in energy is negligible, as it leave earth gravitational field