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Man, I love teaching about electromagnetic waves. Today in intro physics I explained Faraday's law, which says that a changing magnetic field will create an electric field, which may cause current to flow around a loop. I then talked about Maxwell's realization that the opposite should also be true: a changing electric field must create a magnetic field. (It's an algebra-based intro class, so I leave out essentially all the details.) Putting those together, you realize (or at least, Maxwell did) that if the two fields can create each other then they can just travel through space on their own as a wave.
And that's where I found myself starting to literally jump up and down in excitement in class. (Well, only a little.) (Ok, I'll be honest, only a little at first.) Waves were the first topic we covered this semester, so we've come full circle. But then I showed them the speed that Maxwell derived for the waves, written in terms of the force constants for electricity and magnetism (which they've all used and measured in lab). I had students with calculators work out the resulting speed: 3.0 * 10^8 m/s. And wonderfully, in both sections, some student spoke up without any prompting and said, "Isn't that the speed of light?"
That's when I really started jumping up and down and talking rather loud. (Not just a little.) Optics was another big topic earlier this semester, and suddenly we've discovered (following Maxwell) that it's all just electromagnetism! Everything we've done really was all one topic after all! Not only do we know some methods for dealing with light, but we know why light works the way it does. I even had each class come out into the hall, form a line, and act out the part of an electromagnetic wave as they ran past a charged particle (me) and made it oscillate up and down.
It's a good class day, and I always forget how cool the topic is until I'm actually in the process of talking about it.
[And now I wonder: have I posted about this in previous years? 'Cause I totally could have. Ah well... it's cool enough to be worth saying again.]
And that's where I found myself starting to literally jump up and down in excitement in class. (Well, only a little.) (Ok, I'll be honest, only a little at first.) Waves were the first topic we covered this semester, so we've come full circle. But then I showed them the speed that Maxwell derived for the waves, written in terms of the force constants for electricity and magnetism (which they've all used and measured in lab). I had students with calculators work out the resulting speed: 3.0 * 10^8 m/s. And wonderfully, in both sections, some student spoke up without any prompting and said, "Isn't that the speed of light?"
That's when I really started jumping up and down and talking rather loud. (Not just a little.) Optics was another big topic earlier this semester, and suddenly we've discovered (following Maxwell) that it's all just electromagnetism! Everything we've done really was all one topic after all! Not only do we know some methods for dealing with light, but we know why light works the way it does. I even had each class come out into the hall, form a line, and act out the part of an electromagnetic wave as they ran past a charged particle (me) and made it oscillate up and down.
It's a good class day, and I always forget how cool the topic is until I'm actually in the process of talking about it.
[And now I wonder: have I posted about this in previous years? 'Cause I totally could have. Ah well... it's cool enough to be worth saying again.]