Topic 5: Capacitors Flashcards
What is a capacitor?
A capacitor is a passive device that can store electrical charge on plates when connected to a voltage source.
How is a capacitor formed?
A capacitor is formed with 2 conductive plates separated by an insulator layer.
What occurs during the process of charging a capacitor?
Charging of a capacitor occurs when a capacitor is connected to voltage source, positive and negative charges accumulate on the 2 conducting plates.
What is generated by a charged capacitor?
An electric field is generated by the charges on the 2 plates. Along the electric field lines there is a potential change (voltage difference of v_c)
As the electric field (E) increases, what happens to the voltage (v_c) across the capacitor?
As E increases, v_c increases.
How do we define constant capacitance? Under what conditions does this equation work?
Q = CV
Or C = Q/V
It only occurs when balance is reached. Balances refers to when voltage across capacitor is equal to the source voltage (v_s = v_c)
What is the unit of capacitance?
F (Farad)
What is the equation for capacitance between 2 large, parallel plates?
C = (εr.εo)A/L = (εA)/L
where
A = area of either of the 2 plates
l = distance between plates
ε = permittivity of media
εo = permittivity of the vacuum = (8.85)(10^-12) F/m
εr = relative permittivity (dialect constant)
What is the V-I characteristic of a capacitor when provided with the voltage across the capacitor?
What happens when the voltage is constant?`
i(t) = C [(dv(t))/(dt)]
When voltage is constant, the current is 0.
What is the V-I Characteristic of a capacitor when provided with the current?
v(t) = [1/C] [ {integral from t0-t} i(t) dt] + v(t0)
What generates an electric field within a capacitor?
The distribution of charges across a capacitor creates an electric field.
How do you determine the energy stored in a capacitor?
Wc (t) = 1/2 [(C)(v_2)(t)]
How do you determine the equivalent capacitor for multiple capacitors connected in parallel?
Ceq = C1 + C2 + C3 +…..+ Cn
How do you determine the equivalent capacitor for multiple capacitors connected in series?
Ceq = [1/C1] + [1/C2] + [1/C3] +…..+ [1/Cn]
