# How will this help me?

1. Jun 27, 2006

### brent

Hello,
I'm currently helping (I'm the teacher's assistant) with a physics workshop at my college and I haven't even had the course that my teacher says that it will help me in. The workshop is entitled "Visual Quantum Mechanics" and we (me and the teachers that are taking the workshop) have learned alot in the first day of the workshop, but I was just wondering how this will help me with a course entitled Modern Physics? We are studying how LEDs work right now, but I would have thought that maybe this was just a general physics topic. Thanks for the help in advance!

2. Jun 27, 2006

Semiconductors are considered 'modern physics', explainable as they are by quantum mechanics (in a nutshell - wavelength of emitted lightis directly related to the band gap between the p and n type semiconductors that make up the diode).

Consider it a real-life demonstration of e=hf.

3. Jun 27, 2006

### brent

e=hf? also, we covered some more today and I am definately getting the hang of it. I can understand how energy is related to the band gap, but we haven't gotten to the section entitled "Waves of Matter" so I think if we get there I will have a solid grasp on things.

Also, what's the p and n types of semiconductors? That wasn't covered in this workshop. It's more for just the concepts I think.

Thanks again!

4. Jun 28, 2006

Well, can, worms, truly opened!

e=hf describes the relationship between the energy and frequency of a photon. So, higher frequency, higher energy (think X-Rays are considered 'dangerous' whereas visible light generally isn't)

In a semiconductor, n and p type describe a doping process that is applied to the semiconductor to produce excess electrons or holes respectively. By placing n and p type next to each other, a diode is formed as if a current is applied in one direction, these free electrons and holes can 'flow' to the opposite side of the junction (think electrostatics), but if a current is applied in the other direction, no electrons or holes can flow as they are being 'attracted' in the wrong direction, and very few electrons and holes will be produced at the np junction. http://en.wikipedia.org/wiki/Semiconductor gives a much better explaination than I can in a short space, although is rather more verbose.

5. Jun 28, 2006

### brent

Okay, today we're finishing up Solids and Gases, and I'm guessing by n and p you are talking about the pure substance (a semiconductor) that is almost split with two different types of impurities (not sure right now but it said something about one being a donor and one being an acceptor) and when they combine and a voltage is applied in the correct way (so that the acceptor gains enough electrons to connect with the donor) the diode is formed?

By e=hf I was wondering what those variables are. Like I know e=Energy but h=? and f=frequency?

Thanks again!

6. Jun 28, 2006

Staff Emeritus
e is energy as you guessed. f is the frequency (of what? Big question), and h is Planck's constant, a very small number* with the dimensions of energy times time, so when you multiply it by the frequency, dimension one over time, you get the dimensions of energy. The point is that the energy is proportional to the frequency, not the intensity. This is somewhat counterintuitive but it lies at the very heart of quantum mechanics. It was discovered by Einstein in the same year, 1905, that he discovered relativity and e = mc^2.

If we take the frequency to be the frequency of an electromagnetic wave for the moment, then this says the em wave interacts in h-sized chunks, called quanta (plural of quantum, you can take the scientist out of the Latin class, but you can't take the Latin class out of the scientist).

A notation comment. Often you will see this frequency equation with the Greek letter nu insttead of f for the frequency, thus: $$e = h\nu$$. Don't let it throw you, it's the same equation.

*About 6.64 X 10^-34 Joule seconds,if I remember right.

Last edited: Jun 28, 2006
7. Jun 28, 2006

### masudr

Discovered? Or invented...hehe!

8. Jun 28, 2006

Staff Emeritus

He invented the idea, in the same way that Benz invented the carburetor, and he discovered the fact that it explains the photoelectric effect.

9. Jun 29, 2006