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Resistors in Parallel - why the 1/R?

Zs
Hello, Genuinely, I hope this finds you well.


The electrical lessons which I am working on from home are going down well, despite my dodgy diagrams and rather plain English.  They have actually been rolled out to more people which I'm pleased about.  Anyway,  and after each one I get some comments or questions.


in the last one, I covered calculations for resistors.  You know the one for resistors in Parallel which is 1/R = 1/ value of resistor1 + 1/ value of resistor 2 +... and so on...?


Well, one of our ladies has suggested that it would be nice to know the derivation of the 1/R aspect, why it is divided into 1. I expect she already knows because she is a most interesting physicist and I have no doubt her maths is superb.  OMS will have met her.  Good question though. 


Truth is, I'm not sure and I have always rather taken it for granted as something I learned. Care to enlighten me? ...all I can think of is Kirchoff but I would love your advice if you have some time.


Thank you, stay well eh?  

Zs


Parents
  • 0
    In the days of old when the C&G qualification was hard to get with a closed book 21/2 written exam and 4 practical assessments there was often a calculation question around resistances in parallel. Now the  exam has been dumbed down several times to an open book short multiple choice exam no academic effort is required.


    I used to teach resistors in parallel at the start of the course as although the students should have come equipped with this knowledge most did not. I would then set them a question which despite the teaching most got wrong even on one occasion a consultant engineer CEng. Of course it could have been my teaching?


    The exam questions were around a number of circuits connected to a distribution board each with an IR reading of X what was the overall IR for the board and was this acceptable? 


    I will try and dig out an old 2391 question for you all to have a go at , MAPJ is not allowed to play!
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  • 0
    In the days of old when the C&G qualification was hard to get with a closed book 21/2 written exam and 4 practical assessments there was often a calculation question around resistances in parallel. Now the  exam has been dumbed down several times to an open book short multiple choice exam no academic effort is required.


    I used to teach resistors in parallel at the start of the course as although the students should have come equipped with this knowledge most did not. I would then set them a question which despite the teaching most got wrong even on one occasion a consultant engineer CEng. Of course it could have been my teaching?


    The exam questions were around a number of circuits connected to a distribution board each with an IR reading of X what was the overall IR for the board and was this acceptable? 


    I will try and dig out an old 2391 question for you all to have a go at , MAPJ is not allowed to play!
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