Optics B/C

[ichaelm]

Do you have a division B test? Because I doubt that the tests are very similar. Also, do you know if you can take notes to the test like Anatomy?

Actually, that was originally a division B test. I just added the last 3 questions for division C. So if you're in division B, you can just ignore those questions if you'd like.

[brobo]

I downloaded it, and it looks awesome! Thanks ichaelm!

[EpicNguyen8]

Alright, thanks. Just needed something to study/practice off of.

[ichaelm]

Feel free to add your own tests if you want!

[brobo]

Noobish question, I know, but...

Could someone please explain the difference between frequency, wavelength, and photon energy? I don't know if I understand the differences.

[ichaelm]

It's easier to think of waves as waves in a piece of string. So imagine you tape one end of a string to a wall and stand far back, and start waving your hand back and forth. You just made a wave. The frequency is how fast you oscillate. It's measured in cycles per time. But since there's no real unit for a cycle, we just measure it in "per seconds", or hertz. One hertz is equal to one per second, which means you move your hand back and forth one time every second. Pretty simple huh?

So next, you get your friend to take a picture of the string from a side view while you're making the waves. Now you can measure how far apart the peaks of the waves are. That's the same distance as how far apart the troughs are. Because every cycle is the same. And as long as you keep the frequency the same and you're using the same string, the distance between the cycles will be the same too. This distance is called the wavelength. It's just a distance, so we measure it in meters.

Now you do an experiment. You start moving your hand at 1 hertz, and your friend times how long it takes for the first wave to reach the wall. Then you move your hand at 2 hertz, and then 3 hertz, and your friend times the wave each time. And it turns out that all the times are the same! That's because in any given medium, the velocity of a certain type of wave will always be the same.

Now we'll think about this from a mathematical perspective. Basically, v=wf. So if you keep the same medium, so the velocity is constant, then the wavelength and the frequency are inversely related. Basically, the faster you move your hand, the shorter the wavelength is. But they are not the same thing. And the relationship is different for each medium, because the velocity is different.

As for photon energy, do you even need to know that since you're in B division? I ask because it's harder to explain

[brobo]

Wow, that's an awesome explanation! Great!
Well, I would like to know about photon energy, even if it's just a basic example.

[ichaelm]

Well, so for a long time people thought of light as an electromagnetic wave. It acted just like other waves: it underwent reflection, refraction, and diffraction. And while the wave model explained some properties of light, it failed to explain others. Such as why certain elements only absorbed or emitted specific wavelengths of light, and why the photoelectric effect only worked for light above a certain frequency. So some people decided that for those situations, you should think of light as a particle (called a photon), which contains an amount of energy proportional to its frequency. This theory was called the "quantization" of light. It explained all of those phenomena that happen at the atomic scale, or more appropriately, the quantum scale. But you can't explain things like diffraction by thinking of light as a particle. Then, you have to think of it as a wave. So basically, light sometimes acts like a particle, and sometimes like a wave. It has some of the qualities of both. Kinda like a liger.

So a guy named Max Planck, who came up with the modern idea of the photon, also came up with a super simple equation for calculating the energy of a photon. The energy of a photon is equal to its frequency multiplied by a number called Planck's Constant. Actually, it's not just a number; it's a measured value, so it has units too. You can look up its value, I forget it.

[herbblood]

I have read the rules and all...
But can someone simplify the rules a bit because i can't understand them well...

[ichaelm]

You're going to get a test/lab with questions about optics. Then you will have to arrange a mirror and a laser to strike a target in a box.