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Capacitance Questions Help

I'm struggling on how to word/answer a few capacitance related questions.

1. State and explain whether T1/5 = RCLn(5)is supported by your graph (of T1/5 against R).


This is my working out: The gradient of the graph is T1/5 / R
Iv'e re-arranged V = V0e-t/RC
-Ln(V/V0) = t/RC
Ln(V0/V) = t/RC (A - sign switches the fraction inside a Ln function)
t = T1/5 so 5V = V0 , thus T1/5/R = C*Ln(5)

Gradient of the graph = T1/5 / R = C*Ln(5).

But I don't know if that will be enough. I was going to calculate my gradient and since the current is known, I could mathematically prove the gradient = C*Ln(5) but it's only 2 marks =/ Or do I not need this at all and I should mention something about straight line of best fit or about the origin etc?


2. Explain why your points for T1/5 on that graph curve away from the (straight) line of best fit (downwards) as R increases.
(The top 4 points are all below the line slowly getting further away from the line of best fit)

I think this is due to charge leakage as some current could flow across the capacitor plates. Thus, there is less current left in the capacitor to be dissipated and so the readings for T1/5 are less than expected and curve away from the line of best fit. The greater the resistance, the greater the leakage of charge?


3. Suggest and explain a different source of error for those readings.

I was thinking sample rate of the voltmeter, but won't that only be for small values? When R is small, current is dissipated much faster, thus a voltmeter with a small sample rate skips volts resulting in in-accurate readings. But this is for when R is large... Not sure at all tbh.
(edited 8 years ago)
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Reply 1
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Prismere
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Bump - any help?
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dmp1188
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i dont understand what you mean by this question

2. Explain why your points for T1/5 on that graph a curve away from the (straight) line of best fit (downwards) as R increases.
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Prismere
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Edited it to make more sense and remove a typo.

Still need help..anyone?!
Original post by Prismere
Edited it to make more sense and remove a typo.

Still need help..anyone?!
Where do these questions come from? i.e. exam paper/year etc.

You need to post and reference the full question including diagrams otherwise it's all guesswork.
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Prismere
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Original post by uberteknik
Where do these questions come from? i.e. exam paper/year etc.

You need to post and reference the full question including diagrams otherwise it's all guesswork.


It's not an exam paper, rather a set of questions our teacher made and gave us.

The information Iv'e provided is literally all I have, hence why I'm puzzled by it.
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Prismere
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Original post by stupidcupid
Are these prep notes for the physics empa?

Nope, I do ISA's. Either way, Iv'e done all my ISA's - just got 1 AS Physics left which is to do with mechanics.
email me i do not have mechanics isa information. wink wink

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