1 / 22

Quantum Electrodynamics

Quantum Electrodynamics. The Cartoon Version. Placement: Late in the Year. 3 rd day of modern physics unit After units on waves, electricity, and magnetism Prerequisites: Electrical interactions: + and - Photons as quanta of energy Conservation of momentum. Feynman's Idea.

akio
Download Presentation

Quantum Electrodynamics

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Quantum Electrodynamics The Cartoon Version

  2. Placement: Late in the Year • 3rd day of modern physics unit • After units on waves, electricity, and magnetism • Prerequisites: • Electrical interactions: + and - • Photons as quanta of energy • Conservation of momentum

  3. Feynman's Idea • All electric charges love photons and can't get enough of them • "Electric charge" really means "a particle that collects photons" • Charges have different methods of collecting and storing their photons I  photons!

  4. Electric charges collect photons like you and your friends collect DVD's. • You know you love them and can't get enough of them… • You're always on the hunt for more, and yet… • New ones are more valuable than old ones.

  5. Imagine yourself with your DVD's… • Would you like to get a new one for free? How likely is that? • Are you going to give yours up for nothing? Of course not! • But… might it be worth trading that second-season flashback episode that you've never really liked for a mint edition sweeps thriller?

  6. Model 1: Like Charges When photon sharing methods are compatible

  7. An electric charge tooling along… …and meets a like charge. With photons!

  8. How does the interaction go? Never liked this one anyway… Can I have a photon? Hmm... Okay! No. I'll trade you… Never liked this one anyway…

  9. Wait a minute… By conservation of momentum, The exchange should look more like…

  10. The result: Two Like Charges Repel We do NOT see the photon exchange, which occurs too fast for any instrument to measure.

  11. Model 2: Unlike Charges When photon sharing methods are NOT compatible

  12. So here’s our electron, strolling along… When he meets something as unlike as can be! How??? But I have no arms to throw or catch. Want to trade photons? Why don't you come over here so we can both share? Easy! I'll throw, you catch. That is a problem. What do we do? That's a problem! That would be perfect! But neither of us have legs to walk with…

  13. Now let's think hard about that DVD analogy… • Imagine you've just met a fellow collector online. • She's smart, funny, and cool… and she's got all the episodes you've ever wanted. • She's even got a mutual friend to verify that she's not some 40-year-old pervert!

  14. Unfortunately… • She lives in rural Alaska! • You cannot trade. • Your storing and trading mechanisms are incompatible.

  15. Good news! • Both you and your online friend have just gotten huge financial aid packages at your favorite college. • You'll both be going to school together next fall!

  16. And remember… • She's smart, fun, and cool… and you two have the same tastes in everything. • And given that neither of you know anyone else on campus, wouldn't it be a great idea to…

  17. Now for the important part! What are you going to bring? • Clothes • Toiletries • The computer • Winter coat • Books, music… • Oh, yeah… and DVD’s?

  18. Are you really going to have room for your entire DVD collection? What are you going to do?

  19. That's right, you're going to chuck anything that's… • Old • Scratched • Chipped • Not your favorite • Something she's bringing anyway

  20. Now, back to those electric charges… Don’t need THIS anymore… Don’t need THIS anymore…

  21. What do we see? A spark! Hey, look at that!

  22. In conclusion… • Electric charges interact by trading or sharing photons. • Their apparent repulsion or attraction is the result of a "virtual" photon exchange!

More Related