Capacitors Flashcards
What is a capacitor?
An electrical component that stores charge on two parallel separated plates.
Why can’t current flow through a capacitor?
The 2 plates of a capacitor are separated by an insulator such as air.
Define capacitance
The charge stored per unit potential difference.
Define Farad
One Coulomb per Volt
How does a capacitor gain a store of energy?
Due to work done to move a charge Q onto the plates.
What does x represent in the equation X = X0 e^–t/RC ?
Q, V or I
Define time constant
The time taken for the charge (or V or I) to reach e^-1 of any initial value.
What do the letters represent in the formula C = ε0εrA / d = εA / d ?
C - capacitance
εr - relative permissive of the material (insulator)
A - area of each plate
ε0 x εr = ε
εr > 1
What type of relationship is between C and V?
C is inversely proportional to V
The largest C gets the smallest V.
What is the formula for capacitors in series?
1/C = 1/C1 + 1/C2
What is the formula for capacitors in parallel?
C = C1 + C2
What is true about an ideal ammeter and ideal voltmeter?
An ideal ammeter has zero resistance.
An ideal voltmeter has infinite resistance.
If there is no resistance how does this effect a capacitor charging?
It happens instantly.
Why when a capacitor is fully charged and the switch is closed does the charge stay constant?
Because the electrons on the plate create an electric field which is strong enough to resist the flow of electrons from the power supply.
