It’s no secret that electricity isn’t one of my favourite parts of Physics, but there’s no getting away from the fact that it’s very important in our daily lives, so I should try to understand a little more about it. I think it’s so difficult because it’s hard to visualise, but I’m going to try and talk about voltage today, or to give it its scientific name, potential difference.
Now this name is a great clue to what’s going on, and I think voltage as a word should be a little more neglected and potential difference more commonly used. It’s much easier to equate potential difference to potential energy, which is fairly easy to demonstrate. (An object has potential energy if it’s ready to move without further external input, like a squashed spring or a ball held above your head).
So, potential difference is like the amount of potential energy that our electrons in the circuit have. And they get it from the power source, like a battery cell. This force is called Electromotive Force. Obstacles in their way, like bulbs or diodes will take up some of their potential energy.
But we can’t see any of this happening in a circuit, so how do we know? Well, a simple tool called a Voltmeter can show us what’s going on. Connect the voltmeter in parallel (not in series) and it will be able to measure the drop in potential difference over any section of your circuit. So connect it over any of the components, and you’ll get a reading, but connect it in between the components and you shouldn’t get anything at all.
The amount of charge that goes round our circuit (a bit like a measure of its strength, or power) is measured in coulombs. I like to imagine the coulomb like a wheelbarrow, full of strength. As the coulomb goes around the circuit, it has to drop off some of its strength as it goes, which is transferred to the components to make them work.
It gets pretty hard to imagine at this stage, so a summary might be in order to keep us on track. The battery cell provides a potential difference, which gives the electrons potential energy, which in turn means that you have more charge per coulomb going around the circuit. As the electrons encounter components in the circuit they lose charge, which is the same as potential energy, so you can measure the potential difference across the component to see how much voltage they use with a voltmeter. The total potential difference of the components is the same as the potential difference on the battery cell, so the electrons return home to the power supply with no energy and no strength in their coulomb-wheelbarrow.