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Physics/converting farads to surface area

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Question
hello, THIS IS NOT A HOMEWORK QUESTION I AM 38YO!
please tell me how i can work out how many farads would be stored in a sphere of 75cm?
also how big a sphere would be to store a 0.1 microfarad.
THANK YOU,
Gene

Answer
Hello gene,

You seem to be confused about farads. The farad is a unit that describes the coulombs of charge stored on a capacitor as a function of the voltage across the 2 conductors. The formula is
C = q/V
C is the capacitance, measured in farads. For example, the charge on a 0.1 microfarad capacitor, when 10 volts is applied across the 2 leads would be calculated as follows
q = C*V = 0.1*10^-6 farads * 10 V = 1*10^-6 coulombs
So this capacitor would store 1*10^-6 coulombs when it is charged to 10 V. If you double the voltage, it would store twice as many coulombs of charge.

Capacitors have 2 conductors typically a short distance apart. A simple example is 2 parallel plates. As a more difficult example, my Physics book calculates the capacitance, in farads, of a device that is one sphere inside another. When a voltage is applied across the 2 spheres, a charge, in coulombs, is stored.

I hope this helps,
Steve

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Steve Johnson

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I would be delighted to help with questions up through the first year of college Physics. Particularly Electricity, Electronics and Newtonian Mechanics (motion, acceleration etc.). I decline questions on relativity and Atomic Physics. I also could discuss the Space Shuttle and space flight in general.

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I have a BS in Physics and an MS in Electrical Engineering. I am retired now. My professional career was in Electrical Engineering with considerable time spent working with accelerometers, gyroscopes and flight dynamics (Physics related topics) while working on the Space Shuttle. I gave formal classroom lessons to technical co-workers periodically over a several year period.

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BS Physics, North Dakota State University
MS Electrical Engineering, North Dakota State University

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