States of matter

In the previous post I noted how most electricity is generated by the action of turbines transforming mechanical energy into electricity. By far the bulk of those turbines are driven by the motion of steam. Matter exists in three states - solid, liquid and gas. In the solid state the molecules are standing relatively still, in fixed position relative to each other. As such, a solid has both fixed shape and volume. As heat is added, the molecules will vibrate faster and faster, until they reach the point where the energy of the vibration overcomes the forces between the molecules that hold them together, and the molecules slip past each other. This is melting. In the liquid phase, the molecules are still all touching each other, so the volume stays the same, but the shape is variable (that is, when you pour water into a square container, it takes a square shape, but if you pour the same water into a round container it takes a round shape). Now here's the important part for our electricity story: as you add heat to a liquid, eventually the molecules move so quickly they break apart all together and go flying into the air. This is boiling. Since the molecules are not touching in the gas phase, the volume of a gas is variable. As you add heat to a gas, it expands. If you start with liquid water and heat it to boiling, the expanding gas can be directed past a turbine, and the movement of this turbine is what is then used to make electricity. More on the sources of heat tomorrow, but let's give a LEGO representation of the states of matter. After the first and second graders in the Marvelous Multiagers blogger's class had a lesson on the states of matter, some of them created a LEGO version during their playtime. As the teacher describes it, "The big white part is ice. There is a little blue because it's melting a little bit, haha. The big blue part is water. The little white part is a chimney with air coming out of it! We had just talked about how the heating or cooling can change the state of matter, so this really made my day!!". Quick aside - it's pretty much impossible to find a good LEGO image for steam. When you do searches you just come up with train engines and steampunk creations.

Electricity

When you plug your computer, or anything else, into the wall socket, it is extremely probable that the electricity coming through was produced by some sort of electric generator. There are various types, and I'll ignore the differences between AC and DC generators, but all of these depend on a couple of important scientific principles - the conservation of energy and Faraday's law of induction. The conservation of energy states that energy is neither created nor destroyed, but simply changes form. For instance, if I lift the pencil on my desk into the air, my muscles are converting chemical energy from the food I ate into raising the potential energy of the pencil. If I let go of the pencil, that potential energy changes into kinetic energy as the pencil falls. When it hits the desk, you hear the sound, which comes from the kinetic energy of the pencil being converted to the vibrations in the desk and then the air. BTW, this demonstration is much more effective in class if you use a heavy textbook, which tends to wake up dozing freshmen. :) In an electrical generator, the kinetic energy of a spinning turbine (more on what makes that spin in future posts) is transformed into electric current. This is due to electromagnetic induction. In 1931, Faraday described how the motion of a wire relative to a magnetic field leads to a movement of electrons in that wire. If the wire is wrapped around a spinning core between the poles of a magnet (or this can also work if the magnet is doing the spinning).

Redearth76 built this generator using LEGO, neodymium magnets and 30 & 22 gauge wire. He measured 13 volts on the 30 gauge side and 1 volt on the 22 gauge side. He also notes that this is an AC generator, and the LED flashes different colors when positive and negative current is applied, so it blinks back and forth.


Here's another version by goldenbat007


Finally, for a purist version, electric motors work on the reverse of this principle. Instead of using the spinning of an axle to produce an electric current, they use an electric current to produce the motion of an axle. Simple motors can also serve as electric generators, as seen here with a LEGO motor by danky78.