Teaching about electromagnetic radiation & struggling

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Discussion Overview

The discussion centers around the challenges of teaching electromagnetic radiation (EMR) to high school students, particularly in the context of a curriculum that emphasizes the role of accelerating charged particles as the source of EMR. Participants explore various teaching strategies, resources, and the conceptual links between electric and magnetic fields, while expressing concerns about the abstract nature of the topic and the limitations of teaching without advanced mathematics.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested
  • Homework-related

Main Points Raised

  • One participant expresses difficulty in explaining that the source of all EMR is accelerating charged particles, questioning the clarity of the link between this concept and prior discussions on electric and magnetic fields.
  • Another participant suggests that teaching without mathematics is challenging and proposes using experiments to illustrate concepts, recalling a demonstration involving a vacuum tube and AC current.
  • A participant shares a resource for visualizing electromagnetic waves through PhET simulations, emphasizing the importance of understanding the relationship between electric and magnetic fields.
  • Some participants discuss the need for resources aimed at laypeople or high school students, indicating a preference for qualitative explanations over quantitative ones.
  • One participant cautions against oversimplifying the curriculum's assertion about accelerating charged particles, noting that not all light emissions are due to this phenomenon, and suggests exploring historical experiments related to light.

Areas of Agreement / Disagreement

Participants express a range of views on how best to teach EMR, with no consensus on a single effective method. There is acknowledgment of the difficulties posed by teaching without mathematics, and differing opinions on the sufficiency of existing curriculum guidelines.

Contextual Notes

Some participants note the limitations of teaching EMR without calculus, suggesting that this may hinder a deeper understanding of the subject. There are also references to the need for resources that bridge the gap between complex theory and student comprehension.

  • #31
vela said:
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.
 
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  • #32
vanhees71 said:
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?
 
  • #33
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.
 
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  • #34
vanhees71 said:
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?
 
  • #35
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.
 
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  • #36
vanhees71 said:
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.
 
  • #37
Frodo said:
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/
 
  • #38
Frodo said:
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.
 
  • #39
John Kovach said:
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...
 
  • #40
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
 
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