Capacitors Flashcards

Flashcards to review key concepts about capacitors.

Capacitor

An electrical component used to store electric charge, consisting of two metal plates separated by a layer of insulator known as a dielectric.

Dielectric

A non-conducting substance separating the metal plates in a capacitor.

Capacitance (C)

The measure of a capacitor's ability to store charge, defined as the ratio of charge stored to the potential difference between the plates.

C = Q/V

The formula relating capacitance (C), charge (Q), and potential difference (V): C = Q/V.

𝐶 ∝ 𝐴

Capacitance is proportional to the area of the plates.

𝐶 ∝ 1/𝑑

Capacitance is inversely proportional to the distance between the plates.

Dielectric

The insulator between two metal plates of a capacitor.

Functions of Dielectric

It makes sure plates do not contact and increases the capacitance of the capacitor.

Dielectric Constant (εr)

The ratio of capacitance with a dielectric to capacitance without a dielectric.

𝐶 = 𝜀𝑜𝜀𝑟𝐴/𝑑

A constant used to calculate the capacitance when a dielectric material is present between the plates of the capacitor

Capacitors in Series

When capacitors are connected in series, the reciprocal of the resultant capacitance equals the sum of the reciprocals of individual capacitances.

Capacitors in Parallel

When capacitors are connected in parallel, the resultant capacitance is the sum of individual capacitances.

1/𝐶 = 1/C1 + 1/C2 + 1/C3

Formula for effective capacitance of capacitors in series.

𝐶 = C1 + C2 + C3

Formula for effective capacitance of capacitors in parallel.

Energy Stored by a Capacitor

A charged capacitor stores electrical energy in the electric field.

Formula for Energy Stored (U)

U = 1/2 QV

Formula for Energy Stored (U)

U = 1/2 CV^2

Formula for Energy Stored (U)

U = 1/2 (Q^2 / C)

Discharge of Capacitor

The charge on the capacitor and the potential difference across the capacitor decrease with time.

𝑉 = 𝑉0𝑒 − 𝑡/𝐶𝑅

Used to determine the potential difference across a capacitor during discharging.

𝑄 = 𝑄0𝑒 − 𝑡/𝐶𝑅

Used to determine the charge on a capacitor during discharging.

𝐼 = 𝐼0𝑒 − 𝑡/𝐶𝑅

Used to determine the current in a circuit during discharging.

Time Constant (𝜏)

The time it takes for the capacitor to discharge to approximately 36.8% of its initial charge.

Formula for time constant

𝜏 = 𝐶𝑅

Charging of Capacitor

The charge in the capacitor and the potential difference across the capacitor increase with time.

𝑄 = 𝑄0 (1 − 𝑒 − 𝑡 / 𝜏)

Used to determine the charge on a capacitor during charging.

𝑉 = 𝑉0 (1 − 𝑒 − 𝑡 / 𝜏)

Used to determine the potential difference across a capacitor during charging.

𝐼 = 𝐼0𝑒 − 𝑡 / 𝜏

Used to determine the current in a circuit during charging.