GCSE Physics - Series Circuits #17

a common point of confusion in exams is the differences between series and parallel circuits in a series circuit we only have a single loop and the components are all connected one after the other on the other hand parallel circuits contain more than one loop and this small difference completely changes how we measure current voltage and resistance in this video we'll discuss series circuits and some of the calculations that you might have to do then in the next video we'll consider parallel circuits so with this series circuit because all the components are in a single loop

if any one of them is disconnected or broken the whole circuit will stop working this is a really big downside and so in practice very few things are actually connected in series another thing to know is that the potential difference of the cell or battery is shared across all of the components you might sometimes see this shown as an equation like this which just shows that the total voltage is equal to the voltages across all of the individual components so the first component plus the second component and so on so if our battery here had

a potential difference of 12 volts and the only components are these two lamps then the voltage across the two of them must add up to 12. for example if these two lamps were slightly different models and the voltage measured across one of them was eight volts then there must be four volts across the other one as eight plus four is twelve whereas if both lamps were identical and had the same resistance then the voltage must be six across each of them because they would each get half of the 12 volts current meanwhile is the same

everywhere in the circuit no matter where you look we measure courage using an ammeter which we place in series so within the main loop and because the same current flows through all of the components we can put the ammeter anywhere for example instead of putting it down here we could put it up on one of the sides it really doesn't matter we could also calculate the current by dividing the total potential difference by the total resistance which is just a rearranged form of ohm's law resistance is similar to potential difference in that the total resistance

is just the sum of the individual resistances of each component this green symbol just means sum so total and you sometimes see it in physics and maths papers as an example let's imagine that this lamp on the left had a resistance of 4 ohms and the other one had a resistance of 2 ohms the total resistance of our circuit would have to be 4 plus 2 so 6 ohms now that we know the total resistance of our circuit we can use ohm's law to calculate the current by taking the potential difference of our battery so

12 volts and dividing it by a total resistance of 6 ohms to give us a current of 2 amps one thing to be aware of is that ammeters generally have such tiny resistances that we can ignore them in our calculations which is why we haven't included anything for the ammeter the next thing we need to look at is how to calculate the voltage across a single component in a circuit we just worked out that the current in the circuit is 2 amps and remember that with current it doesn't matter whether you're looking at the circuit

as a whole or as an individual component the current is always the same so we can use that current and the resistance of a specific component to find its individual share of the voltage in the circuit for example this lamp on the right has a resistance of 2 ohms and the current across it must be 2 amps so using our ohm's law equation again we can see that the potential difference must be 2 amps multiplied by 2 ohms so there must be 4 volts across this specific lamp to find the voltage across the other component

we could do the same thing again or because we know that the total voltage must be the same as the battery which was 12 volts we could just do 12 minus 4 to find that this other lamp must have a potential difference of 8 volts or if you don't like mats the final way we can find the voltage is just to use a voltmeter which we connect in parallel across the component we're looking at so this one which gives a reading of 8 volts even though voltmeters are in parallel we'd still treat the overall circuit

as being series as a final point it's good to remember that due to ohm's law those components with a greater resistance will always have a higher share of the voltage you can think of this in terms of more force being required to push the charge through the areas of highest resistance this is why our 4 ohm resistor had 8 volts of the overall potential difference but our 2 ohm resistor only got 4 volts anyway that's everything for this video so hope you found it useful and we'll see you soon