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Topic Title: Electrical Principles - AC single phase Circuit
Topic Summary: AC circuits
Created On: 18 December 2012 07:42 PM
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 18 December 2012 07:42 PM
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calumbtw

Posts: 25
Joined: 22 October 2012

Hi,

Have another question! Sorry about posting so many recently. I've got a bit of coursework that I have to do and would like to know if anyone could help me.

A capacitor of 22uF is connected in parallel with a resistor of 75 ohms to a 100v supply at 150Hz. Find the current flowing in the resistive branch and the capacitive branch.

I believe that for the capacitive branch; I = U / Xc. Find out inductive capacitance and then sub into above equation.

Resistive branch; I = U / R.

Thanks for the help.
 19 December 2012 09:14 AM
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ectophile

Posts: 539
Joined: 17 September 2001

Something looks wrong to me on the capacitor side. With the equation you've got, if you increase the value of 'c', then the current 'I' would drop. That's not what would happen.

IIRC, for a capacitor, the impedance is X = 1 / (2 * pi * f * c).

So I = U / X = U * (2 * pi * f * c).

-------------------------
S P Barker BSc PhD MIET
 19 December 2012 09:21 AM
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deleted_1_Grizzly01

Posts: 250
Joined: 21 February 2008

No, the OP is quite correct.

When he's written Xc, that means the capacitive reactance.
You've taken it to mean XC, or X * C, which would be the reactance multiplied by the capacitance. That would be wrong.
 19 December 2012 09:26 AM
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AJJewsbury

Posts: 11268
Joined: 13 August 2003

I took "Xc" to be simply the impedance due to the capacitor (although I'm not sure there's anything inductive about it). Xc = 1/(2πfC)
- Andy.
 19 December 2012 01:21 PM
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ectophile

Posts: 539
Joined: 17 September 2001

Originally posted by: Grizzly01

No, the OP is quite correct.



When he's written Xc, that means the capacitive reactance.

You've taken it to mean XC, or X * C, which would be the reactance multiplied by the capacitance. That would be wrong.


If you put it that way, then it is right. I was trying to read more into it.

-------------------------
S P Barker BSc PhD MIET
 19 December 2012 03:22 PM
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calumbtw

Posts: 25
Joined: 22 October 2012

Sorry I meant capacitive reactance! Thanks for the help all.
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