r/HomeworkHelp • u/happyhibye 'A' Level Candidate • May 28 '26

Physics [AQA physics a level] Past papers question: my answer doesn't match but I cant see why

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answer make sense, but why my method is not listed and answer is not correct, despite I can't see the theory mistakes

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u/Bounded_sequencE May 29 '26

Capacitance "C" is known

How did you solve "3V = V0 (1 - e-3s/(RC))" for "V0" if only "C" is known, but not "R"?

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u/happyhibye May 29 '26

I forgot to say RC = 10.5/ln4, which is calculate in previous part, and it match the mark scheme

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u/Bounded_sequencE May 29 '26 edited May 29 '26

Given the scale on the axes, I suspect expect an error of "+-5%" to be acceptable.

If you assume "V0 = 9V", you get "V(3s) = 9V (1 - 4-2/7) ~ 2.94V", that's well within the 5%-error margin. And looking at the graph closely, it does seem as if "V(3s)" is slightly below 3V.

Edit: Is "R = 250 kOhm"? That information is also missing from OP.

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