Teaching about electromagnetic radiation & struggling

[flintstones]

Ask the students to consider what gets the charges moving to produce the induced current. There has to be some sort of force on them. If they're at rest or there is no magnetic field where the charges are, it can't be a magnetic force, so it has to be an electric force, which implies there must be an electric field.

Thanks! I'll give that a try. I think it'll work well.

 

[bob012345]

To picture a photon as a point-like particle is the most errorneous picture you can teach them!

I assume it's the 'point-like' you object to since every definition I've seen uses the word particle?

 

[vanhees71]

A photon cannot be localized. It's the least particle-like quantum you treat in introductory quantum mechanics. I always emphasize that photons are not like miniature billiard balls and the meaning of the single-photon states as detection probabilities.

 

[bob012345]

A photon cannot be localized. It's the least particle-like quantum you treat in introductory quantum mechanics. I always emphasize that photons are not like miniature billiard balls and the meaning of the single-photon states as detection probabilities.

Ok. Thanks. Could you elaborate a little what you mean by emphasizing the meaning of the single-photon states as detection probabilities. Is it about writing a wave function for the photon state that allows computation of the probability it will be detected in one state as a function of all possible states? Does that imply it is meaningless to talk about a photon apart from a detector unless one knows from a previous experiment what state the photon is in?

 

[Frodo]

Without wading through the thread ...

... my advice would be to get or read a copy of Feynman's Lectures in Physics and all will be revealed. The lectures are mainly written prose as Feynman was a most brilliant teacher who always explained the physics before going on to develop the equations.

I see that some of the lectures themselves are now on line Now, You Can Watch the Feynman Lectures Online For Free so you can see how he explained things.

Also check out Richard Feynman - Science Videos for his lectures on QED - they are breathtaking.

 

[Frodo]

To picture a photon as a point-like particle is the most errorneous picture you can teach them!

Absolutely. How long is a photon? As long as a piece of string.

A photon has a frequency and, (simplistically) to have a frequency, you must have an extended wave with something changing and going up and down.

The more cycles you have in the wave, the more accurately you can measure the frequency; but the more distance the photon extends, and the less accurately you can measure its position. Does it ring any bells? Heisenberg's Uncertainty Principle?

Consider a photon of a long wave radio transmission. If the radio wavelength is 1,500 metres then, simplistically, the photon must be of that order of length.

 

[vanhees71]

Without wading through the thread ...

... my advice would be to get or read a copy of Feynman's Lectures in Physics and all will be revealed. The lectures are mainly written prose as Feynman was a most brilliant teacher who always explained the physics before going on to develop the equations.

I see that some of the lectures themselves are now on line Now, You Can Watch the Feynman Lectures Online For Free so you can see how he explained things.

Also check out Richard Feynman - Science Videos for his lectures on QED - they are breathtaking.

In fact the complete 3-volume set is legally online:

https://www.feynmanlectures.caltech.edu/

 

[vanhees71]

Absolutely. How long is a photon? As long as a piece of string.

A photon has a frequency and, (simplistically) to have a frequency, you must have an extended wave with something changing and going up and down.

The more cycles you have in the wave, the more accurately you can measure the frequency; but the more distance the photon extends, and the less accurately you can measure its position. Does it ring any bells? Heisenberg's Uncertainty Principle?

Consider a photon of a long wave radio transmission. If the radio wavelength is 1,500 metres then, simplistically, the photon must be of that order of length.

What you are vaguely describe is more a coherent rather than a single-photon state. A quantum state which has the properties of a classical em. wave with a definite phase is a coherent state. The photon number is indetermined and Poisson distributed (with the expectation value and standard deviation taking arbitrary positive real values). Indeed there's an uncertainty relation between photon number and phase.

A photon cannot be interpreted as a particle even in the sense as you can interpret the quanta of the massive fields as particles. Any massless quantum with a spin $\geq 1$ does not allow for a proper definition of a position observable. In physical terms: It cannot be localized.

 

[MidgetDwarf]

The comment about control holds. As I think about my hs teachers, they were all dedicated and wonderful, but some commanded respect more than others. Even adults can be cruel to each other. It's in our nature. I don't turn my back to barking dog regardless of any training I've had.

I substituted for one HS physics class. Right away some students started testing me. I ignored them and stuck to their assigned work. The testing continued until one girl spoke up telling the clowns in the class not to harass me because I might be testing them to see if teaching HS physics was worth it. The harassment ended. Recognizing what is honest query and what is not can be more difficult than the subject matter.

I would have kicked them out the class and told I would speak to their guardian... So tell me, if you would like to go down that path? Works every time...

 

[robphy]

Possibly useful:


from https://archive.org/search.php?query=subject:"pssc"

In the video from the Mechanical Universe ( https://en.wikipedia.org/wiki/The_Mechanical_Universe ) below,
although there are equations shown,
"the spatial pattern of the electric and magnetic fields at an instant" is what is important (go to about &t=15m40s) :
focus on Ampere-Maxwell (with the Maxwell term implying a
"curly magnetic field is associated with a time-changing electric field")
and Faraday (implying a
"anti-curly electric field is associated with a time-changing magnetic field").
Together, these laws suggest that
a particular sinusoidal spatial pattern of the electric and magnetic fields
evolves to translate this spatial pattern at a speed 1/\sqrt{\epsilon_0 \mu_0}...
that is, these electromagnetic disturbances propagate at the speed of light