Why won't a bright red light produce a current in a piece of metal as well as a dim blue light? Einstein realised that the only way to explain the photoelectric effect was to say that instead of being a wave, as was generally accepted, light was actually made up of lots of small packets of energy called photons that behaved like particles. Einstein wasn't the first person to use the idea of photons, but he was the first to make it the starting point of an explanation rather than a convenient fiddle to explain away odd results.
With light as photons, Einstein showed that red light can't dislodge electrons because its individual photons don't have enough energy - the impacts are just not large enough to shift the electrons. However, blue light can dislodge electrons - each individual photon has more energy than the red photon. And photons of ultraviolet light, which have yet more energy, will give electrons enough energy to whizz away from the metal altogether. A good way to think of the photoelectric effect is like a full car park with lots of really bad drivers. There is a car parked in a space, and lots of other drivers want that space. To get it they can try knocking the parked car out of the way, but they can only manage to hit it one car at a time. A tiny red mini just won't have the energy to knock the parked car out of the parking space, but a big blue van will. And imagine hitting the parked car with a big ultraviolet lorry - the parked car is most likely going to move far enough to collide with something else. Returning to light and electrons, there is never really just one photon of light at a time. A bright light emits lots of photons, but it doesn't matter how bright a red light gets; red photons will still not be able to budge a single electron. This is like having a car park full of red minis each randomly hitting a parked car in turn - there will be a lot of dents but the parked car will remain where it is. However, even a dim blue light will shift some electrons - we know that even one blue van will be able to move the parked car.
The above article ^ seems to suggest that the amplitude of a dim blue photon, is greater than the amplitude of a bright red photon. IOW, weaker frequencies, like red, have a weaker minimum and maximum amplitude, whereas stronger frequencies, like blue, have a stronger minimum/maximum amplitude. The maximum amplitude of red, is weaker than the minimum capacity of blue. Clear enough.
With that out of the way, I wish to return to a problem raised earlier:
Planck became interested in the problem of accounting for the light and heat sent out by the illumination standard called a ‘black body.’ The black-body was considered the ideal case, and the logic was, if they could understand and predict the ideal case of radiation, then they could go onto to understand the radiation processes in all cases.
Solving the black body problem was to understand how matter produces radiation. It was assumed that the blackbody in its most pure form was some sort of electrically charged particle, the motion of which – speeded up by heat – produced the radiation.
The goal was to assign particular movement of particles to particular kinds of radiation. And to understand how motion of such and such kind yielded radiation of such and such energy.
The trouble came when physicists took the next step; in order to arrive at the distribution of energy in the spectrum, one first had to assign energies to the particles responsible for the radiation - but if energy is continuous, as was assumed, there can be no restrictions on it. [
Restrictions would introduce jumps, abrupt change. Therefore the motions of electrical particles could not be restricted; the motions had to be indefinitely small at the long wave end of the spectrum. But from this it follows inescapably that the radiation energy at the short-wave end will end up indefinitely large. Therefore, restrictions are neccesary. If there are no restrictions, then there will be continuous rise to infinity as motion increases and emitted wave length declines. Physics predicted ultraviolet catastrophe – which is problematic because a glowing body does not radiate an infinite amount of energy.
Honestly, what the hell are they talking about here. I don't understand where this worry about infinitity fits in.
I feel like my new understanding of the photoelectric effect has in no way helped me understand the above.
Experiment shows most of the energy appearing as waves of medium length. The solution is obvious: to avoid the ultraviolet catastrophe and reach an accurate description of black body radiation one must limit the possible energy in such a way that it is not infinite and does not go chiefly to the shortest waves.
Ah, perhaps I'm starting to see now. The empirical data derived from blackbody experiment was suggesting that there is a sudden incline/acceleration in energy concentration as one progresses from red emission to green. (Does the term exponential have any relevence here?) If the rate of increase from red to green, were to remain constant(is this what they mean by continuous?) then, by progressing from green, to blue to ultra violet, the energy would culminate into an ultra-violet collapse into infinity.
??
The assumption of continuous energy made it difficult for Planck and others to see the solution. Black-body measurements were the first evidence that the assumption of unbroken energy was wrong. Energy jumps were apparent.
Is it just me, or does it seem like some visual data is a bit warranted here? I would have liked to have been presented with a theoretical rate of increase responsible for the ultra-violet collapse laid out in an analogy. Maybe a simple sequence of numbers, illustrating some sort of exponential incline/acceleration. Otherwise, its a bit difficult to tell what it is they are talking about.
