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Waves and confusion

Waves and confusion - Physics Forum

Waves and confusion - Physics Forum. Discuss and ask physics questions, kinematics and other physics problems.

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Old 05-09-2004, 08:23 PM
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Default Waves and confusion


A few things mentioned by my A-Level Physics tutor have left me in a
little bit of confusion,

Does the radiation concerned with radio waves (of the frequencies
between 10^3 and 10^10), even comes close to being modeled in quantum
behaviour, or is it concerned with the fields?

Are there any defined point, expecially between the infared and red and
the violet and ultraviolet boundries, where the human eye will just stop
seeing it, or is there a gradient of precieved intensity?

In photoelectric experiments where a reverse PD is applied over the two
plates (making the collecting plate negetive) do the photoelectrons have
to battle their way through the power supply?


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Old 05-09-2004, 10:08 PM
N:dlzc D:aol T:com \(dlzc\)
Posts: n/a
Default Waves and confusion

Dear Danny:

"Danny" <[Only registered users see links. ]> wrote in message

The issue is in detecting their quantum behaviour. Geometries need to be on
the order of the wavelength. Slits need to be many multiples of
wavelengths to be "slits". But detectors for distant objects do indeed
detect and amplify individual radio quanta.

Just as with hearing, different sensory organs have different thresholds.
Even in the same species. And as you note, there is an optimum wavelength
(one of the shades of green) that the human eye is most sensitive to.

You can create enough voltage that the electrons can no longer make it
across the gap. But add more energy, via a shorter light wavelength, and
electrons will be detected again.

David A. Smith

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Old 05-10-2004, 04:49 AM
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Default Waves and confusion

Danny <dan.schofieldremovetosend@virgin.net> wrote in message

Quantum mechanics applies to all known systems, however it is not
needed really unless high accuracy is desired in Most situations. The
exceptions are atomic and similiarly dimensioned problems. Although one
could use QM for radio waves, it isnt really needed unless the utmost in
accuracy is desired. The quantum-like nature of the atomic systems becomes
blurred as the dimensions of the system becomes much larger so that one is
talking about large aggregates of systems. The macroscopic properties that
are measurable are statistical Averages of the quantum features of a system.
Hope that helps a lil.

As you may know, the absorbtion of wavelengths by a atom or molecule is
frequency (v) dependent according to E=hv where h is Plancks Constant and
and E is the energy. That being the case I would expect that the transition
occur rather sharply to very sharply. It could be a bit more distrubuted
dependent upon the exact conditions and constiuency of these molocules that
are involved in the detection of the light. A medical eye doctor would have
the name of these ' devices ' [ cones ?.

The photoelectrons are the electrons which are emitted by a atom or
molecule when the frequency ( E=hv ) is sufficiently high to do so. The atom
has to overcome the ionization energy of the atom to be displaced thusly.
Any additional energy could appear as kinetic energy in the electron. So,
no, these electrons never see the power supply if I understand your
question correctly. You might try and rephrase it. Basically the
photoelectric equation is Nothing more then a restatement of the
Conservation of Energy.


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confusion , waves

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