Electrical circuits

I’ll get top marks for today's homework! I drew the best torch… Hahahaha! What’s that? A torch! - Well, your drawing is really good, but it was a technical drawing that the physics teacher wanted. Ah, great.

Now we can see all the parts. And put them together, according to my technical drawing. - Let’s start with the battery. It’s full of electrically charged particles, shown here as a pink area. They have a negative charge, and they are yearning to get to the positive section of the battery, shown here as blue, to even out the difference in electrical charge. But there is a wall that stops them.

An insulating wall that means a battery can store energy. The positively charged particles are stored on one side of the wall, and the negatively charged particles on the other side. The top and bottom of the battery are called poles. One is positive, and one is negative. In a technical drawing, a single cell battery looks like this.

The long line is the positive pole, and the short one is the negative pole. To get a current -- that is, to get the electrons moving -- the poles must be connected by a conductor. That’s it! Now the electrons can flow. But that’s rather useless, because now all the electrons rush over to the other side, and the battery runs down, without lighting a bulb.

So we add a bulb. We draw it as a circle with an X. Now the current runs from the battery, through the conductor, through the bulb, and back to the battery. It’s important that there is a conductor leading back to the battery. The electrons at the negative pole are longing for the positive pole, but they can’t even start until there is free passage all the way.

When there is free passage, and the electrons can go all the way from the power source back to its other pole, we call it a closed circuit. Now, when we have a closed circuit, the bulb will keep shining, until the battery runs out. But we want to be able to turn the torch on and off. To turn the light off, we need to open the circuit, so that the stream of electrons stops. For that, we use a switch, and it looks like this.

We draw it as a little gate, which can be opened and closed. That way we can control if the circuit is open or closed. We have drawn the symbols for three different parts, or components, of the circuit: A power source -- that’s the battery; a bulb; and a switch. A technical drawing like this, showing how electrical components are connected, is called a circuit diagram. A detail that is sometimes added to a circuit diagram is the direction of the current.

The electrons travel through the circuit, from the negative pole to the positive pole. But here’s a weird thing: We draw the current as if it went from positive to negative. It’s based on an old mistake. At first, when electricity was discovered, scientists thought that it was the positive charge that moved. When it turned out that it was the negatively charged electrons that moved, the formulae were already well established.

And since they worked, people kept the old way of drawing and calculating. It’s an agreement, a convention, that we keep using even though everyone now knows that it’s wrong. -Ok, your torch is better for physics. But we had art homework as well. And there, mine’s the best looking.