Capacitance Flashcards
What is the primary function of a capacitor?
Storing energy.
What are some common uses of capacitors?
Time delay circuits, power smoothing, and protection against surges and spikes.
What is a dielectric in a capacitor?
An electrical insulator placed between the plates to increase capacitance.
How does a capacitor store energy?
By separating charges; one plate holds positive charge (+ve), the other holds negative charge (-ve).
Why is work required to charge a capacitor?
Because charges need to be separated, and energy is released when they come together.
What is the definition of capacitance?
The ratio of charge stored by a capacitor to the potential difference across it.
What is the unit of capacitance?
Farad (F), where 1F = 1 Coulomb per Volt.
What is the formula for capacitance?
C = Q/V, where C is capacitance, Q is charge, and V is voltage.
How does capacitance depend on the physical structure of a capacitor?
Capacitance is directly proportional to the area of the plates and inversely proportional to the distance between them: C ∝ A/d.
What happens during dielectric breakdown?
The electric field strips electrons from atoms in air, making it conductive and resulting in a spark.
Why does dielectric breakdown occur?
Due to high electric fields causing opposite forces on electrons and nuclei in the dielectric material.
How do you calculate total capacitance for capacitors in parallel?
Add the capacitances: C_T = C_1 + C_2 + C_3.
What remains the same for all capacitors in parallel?
Voltage across each capacitor is the same.
How do you calculate total charge stored in a parallel capacitor circuit?
Q_T = Q_1 + Q_2 + Q_3, since charge adds up in parallel circuits.
How do you calculate total capacitance for capacitors in series?
Use the reciprocal formula: 1/C_T = 1/C_1 + 1/C_2 + 1/C_3.
What remains the same for all capacitors in series?
Charge on each capacitor is the same.
How do you calculate the total voltage in a series capacitor circuit?
V_T = V_1 + V_2 + V_3, since voltage adds up in series circuits.
What is the capacitance of a spherical capacitor?
C = 4 π ε_0 r, where r is the radius of the sphere.
What is the formula for the potential of a charged sphere?
V = Q/(4πε_0 r).
How does the capacitance of a sphere change with its radius?
It increases with the radius, as C ∝ r.
What is the formula for energy stored in a capacitor?
W = 1/2 QV = 1/2 CV^2 = 1/2 Q^2/C.
Why is there a factor of 1/2 in the energy formula?
Because the average potential difference during charging is half the maximum voltage.
How is energy stored in a capacitor represented graphically?
It is the area under a charge-voltage (Q-V) graph.
