Syllabus statements 2.1, 2.11, 2.14 - 2.17 Circuits! Ok so first things first, let me introduce you to the simple circuits. Series circuits and parallel circuits.
It's time to talk about Current, Voltage and Resistance in circuits!!!
You probably know the word current from other places, like a current in the sea. It's a similar concept here. Current is a flow of electrons around the circuit. Electrons are the little guys that give the electricity to the components in your circuits. There are loads of them floating around (delocalised) in the copper wires and when you connect a battery they get pushed around the circuit, creating a current. Current is measured in Amperes (shortened to amps), which has a very complicated definition that you don't need to know but I think is quite hilarious for it's complexity. "The ampere is that constant current which, if maintained in two straight parallel conductors of infinite length, of negligible circular cross-section, and placed apart in vacuum, would produce between these conductors a force equal to 2×10−7 newton per metre of length". One crucial thing you need to know about the amp is that 1 amp is a coulomb per second. A coulomb is a measure of charge (seen in chemistry and physics in the equation Q = I x t). So if you have 3 amps flowing through your circuit then you've got 3 coulombs per second going through your circuit. In a circuit if you wan to measure the current you need to include the ammeter into the circuit where you are measuring the current. On to voltage. The fancy name for voltage is potential difference (sometimes shortened to p.d) and this name is one to remember. Voltage is basically the difference in the amount of electricity between two points . This is why voltmeters are connected in parallel to the component you are measuring, as it is measuring the energy before and after the component (potential difference, difference being the difference in electricity between these 2 points), and therefore how much electricity the component is taking. You need to know this - A Volt is a Joule per coulomb. So if my resistor voltage is 5V then it is taking 5 Joules per coulomb, coulomb being of course a unit of charge. Resistance is the easy one. Imagine you're late for physics class and you're running through a corridor full of students, if you're sprinting at full speed you're bound to bump into someone. In this case you represent an electron and the students represent the atoms in the component. This is what happens in just about everything in your circuit, even the wires! This is called electrical resistance. In fact, the only things in the world that can conduct electricity without any electrical resistance are superconductors (no I'm not going into this today). The king of this is the one and only resistor. Resistors can be made from really long wires all coiled (no this is not electromagnetism) into a small space. This long wire has electrical resistance, and when there is a lot of wire, there is a lot of electrical resistance. Resistors reduce the amount of current allowed to flow, the higher the resistance, the less current allowed to flow around the circuit. The unit for resistance is the Ohm which is represented by Ω (yes I know another greek symbol!) Of course there is a formula putting all these together (this is physics remember!) and this is the sweet little formula Voltage = Current (I) x resistance. This law is called Ohm's Law if you were wondering, Ohm as in the unit for measuring resistance. This cute little formula makes it really easy to figure out values in a circuit. Say I have a series circuit that has a light bulb and that's it. The voltage around the light bulb is 5V and 2A is is going around the circuit, what is the resistance of my light bulb? Well rearrange the formula V= I x R to make R = V/I, put the numbers in and boom there we are, the resistance is 2.5 ohms. I'm going to go more into the the calculations next time, but hopefully this has been a pretty solid introduction to circuits and all the units involved. Please let me know in the comments if this this was useful or not, and what I can do to improve! Also if there is any topic in Physics Chemistry or Biology you'd like me to do please comment or send me an email! I'll probably make a video on this too which I will add to this post when I'm done. Once again, I hope you found this useful.
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