## I'm having difficult calculating the capacitance when giving resistance, voltage, hertz, and output amps. Does anyone know how to solve this?

 The question reads: A resistor of 200 ohms and a capacitor of unknown value are connected to a 230 v, 50Hz supply resulting in a current of 0.85A flowing Calculate the value of the capacitor in micro Farads, and show all the working. Okay, so I came to the conclusion that the input current is 1.15 amps, but it says that the output current is 0.85A, how do I account for this with the equation? Thanks by Henrys September 28, 2020 Add comment... Please sign in or create an account to comment.

 Without cap, you are right, it is 230 volt / 200 ohm = 1.15 amp. With a cap, the reactance is not just due to the resistor but also to the cap. The cap "resists" with 1 / (2 pi f C) and when combined with a resistor, both are added using Pythagoras' like theorem for a rigth triangle. So 0.85 amp = 230 volt / ( 200^2 + 1/( 6.28 * 50 hz * C)^2 )^0.5 solved for C gives C = 17. +/- microFarad. The closest standard cap value is 18 microFarad. (Given the usual cap. tolerance, that is the most likely "intended" value). +1 vote by vanderghast September 29, 2020 Technically, I should have use 325 volt p-p to get 230 volt rms but then, I would have not got 0.85 amp as easily spotted (or would have I ? ). Always embarrassing to get the most proper setting, with AC. by vanderghast September 29, 2020 Add comment... Please sign in or create an account to comment.

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