A 4.95 pF parallel-plate air-filled capacitor with circular plates is to be used

Question

A 4.95 pF parallel-plate air-filled capacitor with circular plates is to be used in a circuit in which it will be subjected to potentials of up to 80.0 V. The electric field between the plates is to be no greater than 9800 N/C. As a budding electrical engineer for Live-Wire Electronics, your tasks are to design the capacitor by finding what its physical dimensions must be. As a budding electrical engineer for Live-Wire Electronics, your tasks are to design the capacitor by finding what its separation must be. As a budding electrical engineer for Live-Wire Electronics, your tasks are to find the maximum charge these plates can hold.

Explanation / Answer

First of all we have to calculate the seperation distance d between the plates
E = V/d
d = V/E = 80/9600 = 0.833 cm
Now the capacitance
C = eoA/d
A = Cd/eo = 4.95*10-12*0.833 / (8.85*10-12) = 4.659*10-3 m2
A = r2
r = 6.825 cm
Maximum charge
Q = CV = 4.95*10-12*80 = 3.96*10-10 C

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