# Circuit Lab

### Episode I

-in-the-fingers-

-What is a 'circuit'?

- ) end. When you touch a wire onto both ends of the battery at the same time, you have created a circuit. What just happened? Current flowed from one end of the battery to the other through your wire. Therefore, our definition of circuit can simply be a never-ending looped pathway for electrons (the battery counts as a pathway!).

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-Oh, so I get it Demosthenes, you could just put a wire onto one end of a battery, and the electrons would still bump each other?

No, you could not. As stated before, in our definition of the circuit, a continuous loop is required. But think about it scientifically: If you did attach the wire to only one end of the battery, where would the electrons go that got bumped to the opposite end of the wire? That is why there needs to be that continuous loop of wire: the electrons need somewhere to go.

- -so-

${\displaystyle V=IxR}$

Or

Voltage = Current times Resistance

If you are having trouble, think back to the baseball example: you can have a high chance of winning (voltage) by either scoring a lot of runs (high current) or having good defense/pitching (resistance).

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Have you ever pumped up a super----

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(that last one is more advanced)

### Episode II

A little review, perhaps:

The three concepts of Voltage, resistance, and current are all interrelated through this basic formula:

V = I R

or Voltage = Current times Resistance

Okay, whatever Demosthenes, I don't really care, why do I have to learn this formula anyways? Like I care about this 'omg' guy or whoever he is.

You have to learn Ohm's law because it helps you to 'analyze' circuits. That means you can use this law to find voltage, resistance, or current, if you have two of the three. Let's look at how to apply this formula:

The application of this formula is pretty easy, once you get the hang of it. Basically, imagine a wire, a battery, and a resistor somewhere along the wire. If the battery has a voltage of 10 volts, and the resistor has a resistor of 30 ohms, you simply use Ohm's law to find the current:

V= IR .....write your equation, so you know what you're doing here...

10 volts = (I)(30 ohms) ...Set up the equation, plugging in the values....

(10 volts)/(30 ohms) = I ...Divide both sides by '30 ohms' so that you can isolate the variable, I, or the current....

10 volts/30 ohms = 1/3 amperes do out the math....fun!...

But wait Demosthenes, what if they ask for voltage or resistance?

Don't get scared, my young padawan. The equation can be set up so that no matter which two of the three variables you know, you can figure out the other one easily. Suppose there's a circuit with a 6 volt battery and 2 amps of current, how would you set that up? What's your answer? (You try it first, and see if it agrees with mine!!)

Alright, let's see how you did:

V = IR ....okay, first write out the equation so you know what you're doing

R = (V)/(I) .....Manipulate the equation so you have the two knowns on one side

R = 6 volts / 2 amps ....Plug in the values

R = 3 ohms ....solve by dividing 6 by 2.

Here are the 3 general forms of the law you'll need to know:

V = IR R = V/I I = V/R

Whichever value you're searching for, simply make that the 'lone' variable, then plug in the values, and see what you get. Pretty simple.

There's some nice little quiz questions at the bottom of the page in the following link which you can test yourself further with...

### Episode IV

Okay, we've been talking a lot about resistors - but we don't even know what one looks like yet. The Mighty Resistor

There you have it - pretty simple eh? It's just a piece of metal, and the piece in the center there is what provides the resistance.

But if you think about resistance - remember we said it was the force against the flow of the electrons - you must realize an important concept.

Resistors release heat....Don't worry, I'll explain.

Imagine our electrons - merrily flowing along the wire, pushing new electrons to flow on, and so on. This wire is not very hard to flow in - it's made of a material that's very conductive. But what would happen if we placed something in the middle of the wire that was harder for the electrons to flow through? They're going to be bumping into all the atoms in the material, which will cause the atoms to vibrate. This, in turn, will cause nearby air molecules to take some energy.

That energy is in the form of heat. Where did it come from again? From the electrons bumping into atoms inside the resistor.

But, if you think about this even further, wires are matter too - they have atoms. So you can't say that these are perfect conductors either - because they aren't.

Have you ever wondered why the US government wouldn't just put a bunch of solar panels out in New Mexico, Nevada, and Arizona, then ship the electricity everywhere and make it cheaper for us all? The reason is that electrons can't flow in wires for a really long distance without losing a lot of energy. There's just too many atoms along the way; the amount of energy lost is going to be huge.

That's something very important to realize - and the rules sheet also tells us to pay attention to that.

Despite this, during our calculations with Ohm's Law, we usually disregard wire resistance, because in small circuits the amount of heat energy lost is negligible. However, it's still important to consider.

And what about batteries, the sources of the power which are required for our lovely event?batteries! *cue angel choir music*

Believe it or not - these aren't perfectly efficient either (what kind of world is this?)! The resistance in batteries is also a topic to understand for Circuit Lab. First, let's examine what a battery actually is.

A battery works by producing an excess of electrons through a kind of chemical reaction known as a 'redox' reaction. Basically, without jargon - you have some chemicals inside the battery, they react together, and their reaction creates electrons (we're not concerned with chemistry here, but circuitry). The resistance in a battery comes through the chemicals' ability to react smoothly, and the 'electrode's' ability to get the electrons out smoothly.

In a newer battery, this is not a problem. It is just with older batteries that we find serious internal resistance problems.

These explanations were not meant to have you become the master of science - I just wanted to touch upon some things, because the event rules do. These are some of the more advanced things in the rules - and I'm not looking to explain that in this guide. For further explanations, see the following websites: