Electric Circuits (Yay, I'm psychic!)

Okay, today, I'm going to prove my psychic abilities. I guarantee that what I'm going to talk about now is EXACTLY what Mr. Thompson will talk about on Monday. If you want to sound like an absolute freakin' GENIUS in class on Monday, read on!

Okay, the activity we did yesterday was to help us understand some basic circuit terminology, and more importantly, introduce us to the concepts of voltage, current, and resistance.

So what ARE voltage, current, and resistance?

Electric current is basically made up of flowing electrons (going back to basic chem). It helps to imagine that a wire is a hose, and that the electrons flowing through the wire is the water flowing through the hose.

Voltage (or electromotive force) is defined as the work required to move a charge between two points. Hose comparison: the pressure of the water, or the "pushing force." In English: The phrase "electromotive force" says it all. Electro- (electron) + motive (move) + force = work to move a charge. EMF is measured in Volts. Symbol: v, EMF

Current is the magnitude of the flow of charge. In English: The number of electrons flowing past a point per second. Hose comparison: the amount of water flowing through the hose per second. Current is measured in Amperes (one coulomb/second). Symbol: I (very strange, but true)

Resistance is defined as the opposition of a medium to the flow of electrons. In English:... that's pretty much it. Hose comparison: The tap on a hose, which changes the strength of a hose's pressure without changing the amount of water going through it. Symbol: Ω (Greek letter omega)

These three quantities are interrelated through a relationship called Ohm's law. Resistance is directly proportional to EMF and is inversely proportional to current.

This relationship is:

I * Ω = v

Where I is current, Ω is resistance, and v is voltage/EMF

Drawing a circuit: Tips
1. Wires are straight lines: it makes life less confusing for you. On my robotics team, we often have to make schematic diagrams of electronic and pneumatic systems, and they need to be simple - but accurate. That's exactly what you're shooting for when you draw a circuit diagram- even a moron should be able to read the diagram and know what you're talking about.

2. Make sure that positive and negative terminals are the right way around! A lot of electrical circuits work one way, but not the other- making sure that everything is the right way around is essential.

3. Parallel Circuits Vs. Series circuits: All circuits are NOT created equal. Two bulbs connected in series (left) are NOT the same as two bulbs connected in parallel (right). They have different voltages and current values.

4. Voltmeter position: Don't worry about this yet, but whenever we have to put voltmeters (they measure EMF) in a circuit diagram, they MUST be connected in PARALLEL!!! They tend to "eat" the voltage passing through them... why? Voltmeters have a huge resistance, meaning that there is a large voltage "drop" across a circuit with a voltmeter in it.

5. Use the right symbols: You have a list of electrical symbols in the IB data book thing. Use it!

How light bends

Hey Everyone!

Since Mr. T wasn't here today, I felt that it would be a good idea to talk about all the random light stuff we covered today.

Reflection.
When light tries to enter a new medium at an angle, a portion of the wave's energy is reflected back into the original medium.

The angle that the original ray makes with the normal line is known as the angle of incidence, and the angle that the reflected ray makes with the normal line is the angle of reflection. The most important thing to remember about reflection is that the angle of incidence ALWAYS equals the angle of reflection.

Refraction
Right, so we know that when a wave reaches a new medium, part of the wave's energy just bounces back. What happens to the other part of the light's energy? The remainder of the energy continues on into the new medium, but guess what?

Waves BEND! When light moves from one medium to another, its speed changes, which changes the direction of the wave's travel. This is called refraction.

Note: When objects go from a less "optically dense" medium (i.e. air) to a more "optically dense" medium (water), they bend toward the normal line, but when objects go from a more "optically dense" medium to a less "optically dense" (ex water to air) medium, they bend away from it.

Equations to know and use:

Total internal reflection occurs when none of the light is refracted into the new medium, and all of it is reflected back into the original medium (hence the name). The smallest angle of incidence between 0 and 90 degrees at which this can occur occurs when the angle of refraction = 90 degrees.

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