The key information you need to learn is given here and in the text and image immediately below here. The videos are linked further down this post.
Basically: in series the more
resistors the current has to go through, the greater the total resistance. i.e. in series resistances add up.
In parallel, additional
resistors provide additional paths for the current, so the conductance gets
bigger the more resistors there are.
i.e. in parallel the conductances add up.
In the diagrams below,
- · G is a single conductor that is equivalent to G1 and G2 in parallel
- · R is a single resistor that is equivalent to R1 and R2 in parallel
Here is a good summary - the section on combining resistors starts after 6 mins 50 seconds. (the first section is a good revision about Electrical Power and includes a short section GCSE work on paying for electrical energy). This video explains what is going on really well including some good animations using the Phet circuit modelling software.
In fact, I can't find any videos on the web that show how to combine conductors in parallel - they all use the parallel resistors rule 1/Rtotal = 1/R1 + 1/R2. As you will see if you look at the summary above, this is just the same as Gtotal = G1 + G2, but harder to remember!
Other videos for reinforcement:
I've left these as links instead of embedding - these should let you open the video if you click on teh link. Please let me know what works best.
Extension work for those aiming at the highest grades:
How to solve a complex combination of resistors : https://www.youtube.com/watch?v=9Yv9vrxDvg4&list=PL88B748FA3DA87FD0
Here are the first two above embedded, in case the links don't work
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