All About Capacitor Formula You Need to Know

Capacitors are fundamental components in electronic circuits, storing and releasing electrical energy as needed. Understanding the various capacitor formulas is crucial for designing and troubleshooting circuits effectively.

In this article, we delve deep into the world of capacitors, exploring their types, properties, and the mathematical equations governing their behavior. Whether you’re a beginner or an experienced electronics enthusiast, this guide will equip you with the knowledge to harness the power of capacitors effectively.

What Is A Capacitor

A capacitor is an electronic component used in electrical circuits to store and release electrical energy. It consists of two conductive plates separated by an insulating material called a dielectric. When a voltage is applied across the plates, an electric field forms in the dielectric, causing opposite charges to accumulate on the plates.

This charge separation creates an electric potential difference, or voltage, between the plates. Capacitors are commonly used in various electronic devices and circuits for purposes such as energy storage, filtering, timing, and coupling signals.

Capacitor Capacitance

A capacitor is an electrical component used to store and release electrical energy. It’s made of two conductive plates separated by an insulating material called a dielectric. When a voltage is applied across the plates, an electric field forms in the dielectric, causing opposite charges to accumulate on the plates. This charge separation creates an electric potential difference, or voltage, between the plates.

Capacitance, denoted by the symbol C, is a measure of a capacitor’s ability to store electrical charge for a given voltage. It’s defined as the ratio of the amount of charge stored on one plate of the capacitor to the voltage applied across the plates. Mathematically, capacitance is expressed as:

Where:

• 𝐶C is the capacitance in farads (F)
• 𝑄Q is the charge stored on one plate of the capacitor in coulombs (C)
• 𝑉V is the voltage applied across the plates in volts (V)

The capacitance of a capacitor depends on several factors, including the surface area of the plates, the distance between them (thickness of the dielectric), and the type of dielectric material used.

Capacitance plays a crucial role in many electronic circuits. Capacitors are used for various purposes, such as energy storage, filtering, decoupling, timing, and coupling signals between different parts of a circuit. They can smooth out voltage fluctuations, block DC while allowing AC signals to pass, and store energy temporarily. Capacitors come in various types and sizes, ranging from tiny surface-mount capacitors used in integrated circuits to large electrolytic capacitors used in power supply circuits.

Parallel Plate Capacitor Formula

The parallel plate capacitor formula is used to calculate the capacitance of a capacitor with a simple parallel plate configuration. The formula is derived from the basic principles of electrostatics.

The capacitance (𝐶C) of a parallel plate capacitor is given by the formula:

Where:

• 𝐶C is the capacitance in farads (F),
• 𝜀ε (epsilon) is the permittivity of the dielectric material between the plates, measured in farads per meter (F/m) or in relative permittivity (also known as dielectric constant),
• 𝐴A is the area of one of the plates in square meters (m²),
• 𝑑d is the separation between the plates in meters (m).

This formula shows that the capacitance is directly proportional to the permittivity of the dielectric material and the surface area of the plates, and inversely proportional to the separation between the plates.

For a vacuum or air as the dielectric (𝜀0ε0​), the formula simplifies to:

In this case, 𝜀0ε0​ is the permittivity of free space, approximately 8.85×10−128.85×10−12 F/m.

The parallel plate capacitor formula is fundamental in understanding and designing capacitors, especially those with a simple structure like parallel plate capacitors. It’s used in various applications in electronics, telecommunications, and other fields where capacitors are utilized.

Energy Stored in a Capacitor Formula

The formula to calculate the energy stored (𝑈U) in a capacitor is:

Here’s what each symbol represents:

• 𝑈U is the energy stored in the capacitor, measured in joules (J).
• 𝐶C is the capacitance of the capacitor, measured in farads (F).
• 𝑉V is the voltage across the capacitor, measured in volts (V).

This formula shows that the energy stored in a capacitor is directly proportional to the capacitance and the square of the voltage across the capacitor.

Capacitor Charge Formula

The formula to calculate the charge (𝑄Q) stored in a capacitor is:

Here’s what each symbol represents:

• 𝑄Q is the charge stored in the capacitor, measured in coulombs (C).
• 𝐶C is the capacitance of the capacitor, measured in farads (F).
• 𝑉V is the voltage across the capacitor, measured in volts (V).

This formula indicates that the charge stored in a capacitor is directly proportional to the capacitance and the voltage across the capacitor.

Capacitor Discharge Formula

The formula to describe the discharge of a capacitor over time in a simple resistor-capacitor (RC) circuit is given by:

Here’s what each symbol represents:

• 𝑉(𝑡)V(t) is the voltage across the capacitor at time 𝑡t seconds.
• 𝑉0V0​ is the initial voltage across the capacitor at 𝑡=0t=0, often denoted as 𝑉(0)V(0).
• 𝑒e is the base of the natural logarithm (approximately equal to 2.71828).
• 𝑡t is the time in seconds since the start of the discharge process.
• 𝑅R is the resistance in ohms (Ω) in the circuit.
• 𝐶C is the capacitance in farads (F) of the capacitor.

This formula shows how the voltage across the capacitor decreases over time during the discharge process in an RC circuit. The term 1𝑅𝐶RC1​ is called the time constant of the circuit, representing how quickly the capacitor discharges. As time (𝑡t) increases, the voltage across the capacitor exponentially decreases towards zero.

Capacitor Impedance Formula

The impedance (𝑍Z) of a capacitor in an AC circuit is given by the formula:

Here’s what each symbol represents:

• 𝑍Z is the impedance of the capacitor, measured in ohms (ΩΩ).
• 𝑗j is the imaginary unit, representing the imaginary part of the impedance.
• 𝜔ω (omega) is the angular frequency of the AC signal, measured in radians per second (𝑟𝑎𝑑/𝑠rad/s).
• 𝐶C is the capacitance of the capacitor, measured in farads (F).

This formula indicates that the impedance of a capacitor in an AC circuit is inversely proportional to the product of the angular frequency (𝜔ω) and the capacitance (𝐶C). As the frequency of the AC signal increases, the impedance of the capacitor decreases, allowing more current to flow through it. Conversely, at lower frequencies, the impedance increases, restricting the flow of current.

The negative sign in the denominator represents the 90-degree phase shift between the voltage across the capacitor and the current flowing through it in an AC circuit. This phase shift occurs because the current leads the voltage in a capacitor.

Capacitor in Series Formula

The formula to calculate the total capacitance (𝐶totalCtotal​) of capacitors connected in series is given by:

Here’s what each symbol represents:

• 𝐶totalCtotal​ is the total capacitance when capacitors are connected in series, measured in farads (F).
• 𝐶1,𝐶2,𝐶3,…C1​,C2​,C3​,… are the capacitances of individual capacitors connected in series, also measured in farads (F).

This formula shows that when capacitors are connected in series, the reciprocal of the total capacitance is equal to the sum of the reciprocals of the individual capacitances. As a result, the total capacitance of capacitors in series is always less than the smallest individual capacitance.

When capacitors are connected in series, their effective capacitance decreases due to the increased overall distance charge carriers must travel.

Parallel Capacitor Formula

The formula to calculate the total capacitance (𝐶totalCtotal​) of capacitors connected in parallel is:

Here’s what each symbol represents:

• 𝐶totalCtotal​ is the total capacitance when capacitors are connected in parallel, measured in farads (F).
• 𝐶1,𝐶2,𝐶3,…C1​,C2​,C3​,… are the capacitances of individual capacitors connected in parallel, also measured in farads (F).

This formula shows that when capacitors are connected in parallel, the total capacitance is equal to the sum of the capacitances of the individual capacitors. As a result, connecting capacitors in parallel increases the total capacitance, as each capacitor contributes to the overall capacitance.

Voltage Capacitor Formula

The formula to calculate the voltage (𝑉V) across a capacitor in a DC circuit is:

Here’s what each symbol represents:

• 𝑉V is the voltage across the capacitor at time 𝑡t seconds.
• 𝑉0V0​ is the initial voltage across the capacitor at 𝑡=0t=0, often denoted as 𝑉(0)V(0).
• 𝑒e is the base of the natural logarithm (approximately equal to 2.71828).
• 𝑡t is the time in seconds since the start of charging or discharging the capacitor.
• 𝑅R is the resistance in ohms (Ω) in the circuit.
• 𝐶C is the capacitance in farads (F) of the capacitor.

This formula describes how the voltage across a capacitor changes over time during the charging or discharging process in a DC circuit. The term 1𝑅𝐶RC1​ represents the time constant of the circuit, indicating how quickly the capacitor charges or discharges. As time (𝑡t) increases, the voltage across the capacitor approaches 𝑉0V0​, the maximum voltage in a charging circuit or zero in a discharging circuit.

Spherical Capacitor Formula

The capacitance (𝐶C) of a spherical capacitor can be calculated using the formula:

Here’s what each symbol represents:

• 𝐶C is the capacitance in farads (F).
• 𝜀ε (epsilon) is the permittivity of the surrounding medium, measured in farads per meter (F/m).
• 𝑎a is the radius of the inner spherical conductor (in meters).
• 𝑏b is the radius of the outer spherical conductor (in meters).

This formula is applicable when the space between the concentric spherical conductors is filled with a homogeneous dielectric material of permittivity 𝜀ε. The capacitance of a spherical capacitor is influenced by the radii of the two conductors and the permittivity of the dielectric material between them.

FAQs about Capacitor Formula

Conclusion:

Mastering capacitor formulas is essential for designing and analyzing electronic circuits effectively. By understanding the principles and equations governing capacitors, you can unlock their full potential in a wide range of applications. Whether you’re a student, hobbyist, or professional engineer, the knowledge shared in this article will empower you to harness the power of capacitors with confidence.

For all capacitor formulas, please feel free to contact us at any time.