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Cruckshank
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http://papers.xtremepapers.com/AQA/P...W-QP-Jan02.pdf
Question 1a on this paper is a bit weird. I haven't come across the idea that if you have a resistor and wire (assume no resistance?) in parallel, the current will totally avoid the resistor, and just flow through the wire.
I have two problems with this:
1) Why, in alternate circuits, does the current simply not 'avoid' the higher resistance parallel components. I.e. opt to flow through a 10ohm resistor rather than a 20ohm resistor (when in parallel).
2) Has this concept been removed from the specification? I have completed all Physics A AQA unit 1 past papers on electricity, and have never seen anything of the sort - I'm simply worried that this type of question (linked above) will appear in June, and take me by surprise.
Question 1a on this paper is a bit weird. I haven't come across the idea that if you have a resistor and wire (assume no resistance?) in parallel, the current will totally avoid the resistor, and just flow through the wire.
I have two problems with this:
1) Why, in alternate circuits, does the current simply not 'avoid' the higher resistance parallel components. I.e. opt to flow through a 10ohm resistor rather than a 20ohm resistor (when in parallel).
2) Has this concept been removed from the specification? I have completed all Physics A AQA unit 1 past papers on electricity, and have never seen anything of the sort - I'm simply worried that this type of question (linked above) will appear in June, and take me by surprise.
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uberteknik
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(Original post by Cruckshank)
Question 1a on this paper is a bit weird. I haven't come across the idea that if you have a resistor and wire (assume no resistance?) in parallel, the current will totally avoid the resistor, and just flow through the wire.
I have two problems with this:
1) Why, in alternate circuits, does the current simply not 'avoid' the higher resistance parallel components. I.e. opt to flow through a 10ohm resistor rather than a 20ohm resistor (when in parallel).
Question 1a on this paper is a bit weird. I haven't come across the idea that if you have a resistor and wire (assume no resistance?) in parallel, the current will totally avoid the resistor, and just flow through the wire.
I have two problems with this:
1) Why, in alternate circuits, does the current simply not 'avoid' the higher resistance parallel components. I.e. opt to flow through a 10ohm resistor rather than a 20ohm resistor (when in parallel).
Short circuits are 'idealised' zero resistances which makes qualitative analysis and close approximation calculation a lot easier. In reality, even short-circuits have a small finite resistance.
I = V/R
As resistance tends to zero, current approaches infinity and clearly this cannot happen. Current is limited by the conductors finite resistance.
In a parallel circuit, the pd across all parallel paths is the same. The current through each path is still determined by the I = V/R relationship through individual paths and the total current entering and leaving the common parallel junctions is the sum of currents in the individual paths.
With a short circuit in the real world, the short circuit resistance means that the current through the s/c path is far greater than the current through the adjacent high resistance path/s. The parallel currents still sum nevertheless.
It's just easier for a qualitative analysis to 'assume' all the current flows down the s/c path. In reality this cannot happen.
(Original post by Cruckshank)
2) Has this concept been removed from the specification? I have completed all Physics A AQA unit 1 past papers on electricity, and have never seen anything of the sort - I'm simply worried that this type of question (linked above) will appear in June, and take me by surprise.
2) Has this concept been removed from the specification? I have completed all Physics A AQA unit 1 past papers on electricity, and have never seen anything of the sort - I'm simply worried that this type of question (linked above) will appear in June, and take me by surprise.
This question is not one of them.
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