Now, boys and girls. I’m going to tell you a story. Are you sitting comfortably? Then I’ll begin.
Inside a cell (the thingy you use inside the TV remote to make it go – if there’s two of them then it’s called a battery – ) there’s a guy with one of these. You don’t believe me? I promise you, it’s true!
Or, if you like – have a look here. This is an interactive simulation so you can play with it
His job is to keep the + and – charges inside separate He’s a charge shoveller, in other words It takes a lot of energy to keep the charges separate. It’s written on the cell exactly how much – 1.5V, or 1.5 joules for each coulomb, the EMF of the cell. If there’s a wire connecting the + and -, like a back door, the – charges get to sneak out through the back door and round to get to the + charges, using up energy as they go.
Mr Coulomb is a backpacker who often visits the cell.
Here he is, having just passed through the cell, which is his energy shop to fill up his backpack with energy.
He strides off round the circuit. At first, he’s just walking on a nice flat level road, which doesn’t use up much energy. Then he gets to one of these.For him it’s like climbing a very steep hill and he has to use almost all the energy in his backpack to get through the bulb. Meanwhile, the bulb cheerfully converts his electrical energy into heat and light. Poor old Mr Coulomb. He’s worked hard and he needs to get back to the battery to fill up his backpack again. Off he goes, back to the battery for some R&R and a new backpack.