A 4.90pF parallel-plate air-filled capacitor with circular plates is to be used

Question

A 4.90pF 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 115V . The electric field between the plates is to be no greater than 9750N/C .

A. As a budding electrical engineer for Live-Wire Electronics, your tasks are to design the capacitor by finding what its physical dimensions must be.?

B. As a budding electrical engineer for Live-Wire Electronics, your tasks are to design the capacitor by finding what its separation must be?

C. As a budding electrical engineer for Live-Wire Electronics, your tasks are to find the maximum charge these plates can hold?

Explanation / Answer

A. apply C = eoA/d

here apply E = V/d

so d = V/E = 115/9750 = 0.0117 m

so

Area A = Cd/eo

A = 4.9 e-12 * 0.0117/(8.85e-12)

A = 6.477 *10^-3 m^2

ARea = pi r^2 = 0.006477

r^2 = 0.00647/3.14    = 0.0206

r = 45.41 mm

----------------------------

Apply E = V/d

so d = V/E = 115/9750

d   = 0.0117 m or 1.17 cm

---------------------------
apply Qmax = CV

Qmax = 4.9 e-12 * 115

Qmax = 563.5 pC

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