So today in Physics we've moved onto the topic of electricity which I'm happy about as it contains what I learnt in Electronics. We covered the basic principle that:
In a series circuit, PD is split among components and current is the same anywhere in the circuit
In a parallel circuit, PD is the same among components and current is split
One of my friends didn't understand why this happens and turned to ask me to explain. Little did he know that my way of explaining was with dwarves. So when I started off with 'Well, I imagine the charge going round the circuit as the dwarves in Snow White and the Seven Dwarves marching around their mine...' I did get a very strange look.
Anyway this is my explanation:
So there is a line full of dwarves carrying sacks that march around in a circuit. Each dwarf represents a charge.
When they get to the source of jewels (represents the battery), they fill their sack with a jewel (the red stone in the dwarf's sack). This represents the PD. So the 'dwarf' is carrying the 'jewel'. The charge is carrying a PD that it gained from the battery.
When the dwarf gets to a collection chute, it dumps the jewel it has collected into it so that it can be sucked away. So, the charge then passes the PD to the component so that it can be used up.
Then the dwarf makes his way back to the source of jewels and repeats the process again. The charge goes back to the battery.
However there is a continuous line of dwarves. They are the current, as current is the rate of flow of charge.
So in a series circuit, the current is the same throughout. This is because all the 'dwarves' are following the same route so the rate of flow of charge is the same everywhere.
However, the reason the PD is shared between the components is because when there are two 'delivery chutes', the 'dwarves' have to put half their innings in one chute and the other half in the other chute, to make sure their goods are evenly distributed. (I guess we just have to imagine that the dwarves can split a jewel in two without any effort. We're already imagining dwarves as it is!) So, the charge gives half its PD to one component, the the other half to another (we're assuming the components have the same resistance. If resistance is different, the proportion of PD that each component will receive is changed). However, if there are 3 components, the PD will split 3 ways; 4 component, PD splits 4 ways etc.
Now onto a parallel circuit. Here, the current is split. This 'mine' has two pathways each containing a 'collection chute'. So the line of 'dwarves' split in two - half go one way and the other half take the other path (they split in half assuming that both components have the same resistance. Again, if resistance is different, the proportion of the split of 'dwarves' will be different). Therefore, the rate of flow of charge is smaller than the current next to the battery. Both currents in the branches add up to make the total current (next to the battery). If there are 3 branches, the troop will split I'm 3; 4 branches, split in 4 etc.
However, the PD remains the same among both components because each 'dwarf' is still carrying one 'jewel' which it dumps off at its respective 'collection chute'. There's no need to split the 'jewel' in half as the 'dwarves' have split their troop in half. So the component receives the full 'jewel'.
Well, I hope this makes sense! I'll put a little key below. It'll be interesting and useful to look back at this when I need to revise or later in life. Maybe I can even direct my sister to this one day!
'Mine' - circuit
'Dwarf' - charge
'Source of jewels' - battery
'Jewel' - PD/Voltage
'Line of dwarves' - current
'Collection chute' - component
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