A multi plate variable capacitor has 4 pair of plates. The plates, when closed, are separated in air by 0.01mm and a capacitance range of 10 to 400pF.
a) Estimate the required radius R of each plate.
b) The capacitor is set to maximum 400pF and is charged to 10V through a 50kΩ resistor. Determine:
i) The initial value of the current flowing.
ii) The time constant for the circuit.
C = εr εo A (n-1)/d
The Attempt at a Solution
I am still new to all this so please dont go too technical with any replies.
I think the correct formula to work out the radius is C=εr εo A (n-1)/d
Transpose this to make A the subject:
A= Cd/εr εo (n-1)
Which gives me A= (400x10^-12)x(0.00001)/1 x 8.85x10^-12 x 7
Area of plate = 0.00316 (I think this is meter^2)
Then use this answer in A=∏r^2
Transpose for radius = √A/∏
Which gives me an answer of 0.0317 (Again I think this is meters).
bi) The initial value of current flowing.
If t=0 The charging current has its highest value.
bii) The time constant t=CR
Could you tell me if I am going about these the correct way or am I way off mark thanks.