Original post by username17263528
https://isaacphysics.org/questions/resistive_shape?stage=a_level
I’m stuck on part b, and this is probably also preventing me from getting a correct answer for part c as well. I would really appreciate some help; I will attach my working below as a photo.
I’m stuck on part b, and this is probably also preventing me from getting a correct answer for part c as well. I would really appreciate some help; I will attach my working below as a photo.
The resistance per unit length is 6 ohms per meter, not per cm.
Original post by username17263528
I’m now stuck on part c. I calculated the total resistance of the semicircular part including the 5cm bit (because the current going through that branch will be the same) as 6(5pi x 10^-2 + 5 x 10^-2) = 1.242477796. Then because the potential difference is the same across each branch, the potential difference across the semicircular part including the 5cm bit is the same as the potential difference across the two legs (the 5cm + 5sqrt(2) cm bit). The potential difference across the two legs is 100 x 10^-3(0.06(5 + 5sqrt(2))/(0.06(5 + 10 + 5 + 5 sqrt(2)), which is 0.04459029062V, but then when I do V/R = I, this does not give me the correct answer. Can anyone see where I am going wrong? Thank you.
Is worth doing a sketch and uploading that. But you have 3 resistors in series (one is an equivalent resistance from the two parallel paths) with total resistance R and you get the current in the circuit from V/R. Then get the pd across the parallel paths. You cant just consider one leg as you seem to be doing, as the current in that path is different / youre assuming the current in the arc path is zero. Then get the current in the arc from that resistance and pd across it.
(edited 7 months ago)
Original post by username17263528
Hahaha oh dear, thanks for pointing that out and for your help with the method, I’ve got the correct answer now.
You realise that when I suggested drawing it, I meant the relevant, equivalent circuit(s) which you can annotate with appropriate info. Might help to stop typo errors like this.
(edited 7 months ago)
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