Capacitor and Capacitance

Capacitor and Capacitance - Formula, FAQs

Edited By Vishal kumar | Updated on Jul 02, 2025 04:45 PM IST

This article gives the solution for what is a capacitance of a capacitor, what is a capacitor used for, and on what factors the capacitance of a capacitor depends. The concept of capacitance or capacitor formula, the difference between capacitor and capacitance are also mentioned here. It also explains the relation between q, c, and v.
Note: Capacitor meaning in Tamil is மின்தேக்கி

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Capacitor basics:
What is the capacitance of a capacitor?
How does a capacitor work?
Difference between capacitor and capacitance:

Capacitor and Capacitance - Formula, FAQs

Capacitor basics:

The capacitor was called condensers in the earlier days by Alessandro Volta. As the device stores a higher density of electric charge than the isolated conductor, the condenser term was used. This name is still used in automobile systems and other higher applications now also. Later in 1975, scientist Ewald Georg von Kleist invented the capacitors. But there were no records for his invention. Then, a device called the Leyden Jar was introduced by Dutch scientists and it was named the first capacitor.

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What do you mean by capacitor?

A device that stores electrical energy is called as a capacitor.

What is the capacitance of a capacitor?

The ability to store electrical energy in the form of charge is called the capacitance of a capacitor. Capacitance is also defined as the ratio of charge Q and the potential across the capacitor V. Capacitance formula is given by,

Capacitance, $C=\frac{Q}{V}$

Farad (F) is the SI unit of capacitance.

How does a capacitor work?

A capacitor consists of two conductors separated by an insulator. The insulators used in the capacitor are glass, ceramic, air, etc. They are also called dielectric materials. The capacitor’s capacity to store charge is increased by the insulators. The capacitor is used as high voltage and low voltage appliances depending on the type of dielectric used in the capacitor.

Capacitance of a capacitor with air as dielectric material

Figure 1 Capacitance of a capacitor with air as dielectric material

The capacitor plates are connected to the negative terminal of the battery. Then the electrons produced by the battery are received by the capacitor plates. The capacitor plates that are connected to the positive terminal of the battery lose electrons to the battery. The capacitor will have the voltage same as the battery when it is charged completely.

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Let C be the capacitance of a capacitor and V be the potential difference. Then, the amount of charge or electrons that move into the plates is given by the formula,

Q=CV

Unit of charge Q: Coulomb C

Unit of capacitance C: Farad F

Unit of potential across the capacitor V: volts

The above formula is called the capacitor formula or capacitance-voltage formula.

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How to calculate the capacitor value in the circuit?

In a series circuit, the charge across each capacitor is equal to the total charge in the series circuit. Therefore, the capacitor value in the series circuit is calculated by the formula,

1/C_total=1/C₁+1/C₂+1/C₃

In a parallel circuit, the voltage across each capacitor is equal to the voltage in the parallel circuit. Hence, the capacitor value in a parallel circuit is calculated by,

C_total=C₁+C₂+C₃

What is capacitor current?

The rate of change of voltage across the capacitor with time is called the capacitor current.

Capacitor current formula is given by,

$i=c\tfrac{dv}{dt}$

Capacitance concentric spheres:

A spherical capacitor is made up of a hollow or a solid spherical conductor with another concentric spherical conductor encircled by it. The capacitance of the concentric sphere is, $C=4\pi \varepsilon_0R$

Here, ε₀is the permittivity of free space, and R is the radius of the sphere

Capacitor chart or capacitance table:

The capacitor chart gives the capacitance value with the help of a certain code. The first two digits in the code are represented in picofarad units. The third digit is the multiplier. A code with only two digits has capacitance values only in picofarad or pF.

NCERT Physics Notes :

Give two factors that affect the capacitance of a capacitor

The electrostatic capacitance depends on the following factors:

Size of the conductor plate
Insulator or dielectric inserted in between the conductors

Mention the types of capacitors with images.

Different types of capacitors

Figure 2 Different types of capacitors

Types of capacitors are,

Ceramic capacitors
Electrolytic capacitors
Non-polarized capacitors
Film capacitors

Difference between capacitor and capacitance:

There is not much difference between a capacitor and a capacitance.

A capacitor stores the electrical charge whereas capacitance is the capacity of the device to store the charges.
Capacitance is observed in between two conductors while a capacitor is a device constructed to increase the charge storing ability.

What is a capacitor used for?

The capacitor is widely used in the field of electronics. Capacitors with varying current capabilities, temperature coefficients, and stability levels are used in different applications.

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Frequently Asked Questions (FAQs)

1. What is capacitor capacity?

The capacity of the capacitor is the capacitance of the device to store the charge.

2. What is the relation between capacitance and voltage?

From the capacitance formula, we can say that capacitance is inversely proportional to the voltage across the capacitor.

3. Describe electrical capacitor function.

The basic function of the capacitor is to store energy in the form of an electric charge.

4. Name the dielectric used in supercapacitors.

Supercapacitors use an anode from an electrolytic capacitor as a dielectric which has higher dielectric strength.

5. A battery is used to charge a parallel plate capacitor until the potential difference across the conductors is equal to the emf of the battery. The ratio of the energy stored in the capacitor and the work done by the battery is:

1/2

6. The ability of a capacitor to store charge depends upon what factors?

The ability of a capacitor to store charge depends on the dielectric constant of the material.

7. On what factors capacitance of a capacitor does not affect?

The capacitance of a capacitor is not affected by the type of material of the conductor plate.

8. What do you mean by a charge on the capacitor plates is increasing?

Increasing the charge on the plates of a capacitor means the voltage across the plates is increased.

9. How long can a capacitor hold a charge?

In general, a capacitor that is charged for up to 20 seconds can hold the charge for about 40 minutes.

10. What is the charge on the capacitor in steady-state?

Zero

11. What is the difference between a polarized and non-polarized capacitor?

Polarized capacitors have a specific positive and negative terminal and must be connected in the correct orientation. They are typically used in DC circuits and can be damaged if connected backwards. Non-polarized capacitors can be connected in either direction and are commonly used in AC circuits. The main difference lies in their internal construction and the type of dielectric used.

12. What is the purpose of a decoupling capacitor in electronic circuits?

A decoupling capacitor, also known as a bypass capacitor, is used to reduce noise and stabilize power supply voltages in electronic circuits. It acts as a local energy storage device, providing a quick source of current for integrated circuits when they need it. This helps to:

13. What is meant by the "self-discharge" of a capacitor?

Self-discharge refers to the gradual loss of stored charge in a capacitor over time, even when it's not connected to a circuit. This occurs due to imperfections in the dielectric material and small current leakages. The rate of self-discharge depends on the capacitor type, quality, and environmental conditions. It's an important consideration in applications where long-term charge storage is required.

14. How do electrolytic capacitors work and what are their advantages and disadvantages?

Electrolytic capacitors use an electrolyte solution as one of their plates:

15. What is dielectric absorption in capacitors and why is it important?

Dielectric absorption, also known as dielectric relaxation, is a phenomenon where a capacitor that has been discharged briefly and then open-circuited will gradually develop a small voltage across its terminals. It's important because:

16. Why are farads considered a large unit for capacitance?

Farads are considered a large unit because most practical capacitors have capacitances much smaller than 1 farad. Common capacitors typically have capacitances in the range of microfarads (μF), nanofarads (nF), or picofarads (pF). A 1-farad capacitor would be physically very large and is rarely used in everyday electronics.

17. How do supercapacitors differ from regular capacitors?

Supercapacitors, also known as ultracapacitors, differ from regular capacitors in several ways:

18. How does the concept of capacitance apply to the human body?

The human body can act as a capacitor:

19. What happens to the capacitance when two identical capacitors are connected in series?

When two identical capacitors are connected in series, the total capacitance decreases. For two identical capacitors with capacitance C, the equivalent capacitance (Ceq) is half of the individual capacitance: Ceq = C/2. This occurs because the effective plate separation increases, reducing the overall capacitance. The formula for n identical capacitors in series is 1/Ceq = n/C.

20. How does the capacitance change when two identical capacitors are connected in parallel?

When two identical capacitors are connected in parallel, the total capacitance increases. For two identical capacitors with capacitance C, the equivalent capacitance (Ceq) is twice the individual capacitance: Ceq = 2C. This happens because the effective plate area increases, enhancing the overall capacitance. The formula for n identical capacitors in parallel is Ceq = nC.

21. What is a capacitor and how does it work?

A capacitor is an electrical device that stores electric charge. It consists of two conducting plates separated by an insulating material called a dielectric. When connected to a voltage source, opposite charges accumulate on the plates, creating an electric field in the dielectric. This field stores electrical energy, which can be released when needed.

22. How does inserting a dielectric material between capacitor plates affect its capacitance?

Inserting a dielectric material between capacitor plates increases its capacitance. The dielectric reduces the electric field strength between the plates, allowing more charge to be stored at the same voltage. The increase in capacitance is proportional to the dielectric constant (κ) of the material. The new capacitance is C = κC₀, where C₀ is the capacitance without the dielectric.

23. How does a variable capacitor work?

A variable capacitor, also called a tuning capacitor, allows its capacitance to be adjusted mechanically. It typically consists of two sets of metal plates: a fixed set and a movable set. By rotating a shaft, the overlap area between these plates changes, altering the capacitance. This design is based on the principle that capacitance is proportional to the plate area. Variable capacitors are often used in radio tuning circuits.

24. How does energy storage in a capacitor differ from energy storage in a battery?

Capacitors store energy in an electric field, while batteries store energy through chemical reactions. Capacitors can charge and discharge very quickly but store less energy per unit volume compared to batteries. Batteries can store more energy but charge and discharge more slowly. Capacitors are better for short-term, high-power applications, while batteries are suited for long-term, steady power needs.

25. What is meant by the "breakdown voltage" of a capacitor?

The breakdown voltage, also known as the dielectric strength, is the maximum voltage a capacitor can withstand before its dielectric material fails and becomes conductive. When this voltage is exceeded, the insulating properties of the dielectric break down, potentially causing permanent damage to the capacitor. Operating a capacitor near or above its breakdown voltage can lead to short circuits and component failure.

26. How is capacitance defined and what is its unit?

Capacitance is defined as the ratio of the charge stored on a capacitor to the potential difference between its plates. It is measured in farads (F), where 1 farad equals 1 coulomb per volt. The formula is C = Q/V, where C is capacitance, Q is charge, and V is voltage.

27. What factors affect the capacitance of a parallel plate capacitor?

The capacitance of a parallel plate capacitor depends on three main factors:

28. What is the significance of the dielectric constant in capacitor design?

The dielectric constant (κ) is a crucial parameter in capacitor design:

29. What is the time constant of an RC circuit and how is it related to capacitor charging?

The time constant (τ) of an RC (Resistor-Capacitor) circuit is defined as the product of resistance (R) and capacitance (C): τ = RC. It represents the time it takes for the capacitor to charge to about 63.2% of its full charge or discharge to about 36.8% of its initial voltage. After five time constants, the capacitor is considered fully charged or discharged (to within 1% of its final value). This concept is crucial for understanding the charging and discharging behavior of capacitors in circuits.

30. How does temperature affect the performance of a capacitor?

Temperature can significantly impact a capacitor's performance. Higher temperatures can:

31. What is the significance of equivalent series resistance (ESR) in capacitors?

Equivalent Series Resistance (ESR) is a crucial parameter in capacitor performance:

32. What is the concept of capacitor self-resonance and why is it significant?

Capacitor self-resonance occurs when a capacitor behaves like an inductor:

33. How does the concept of displacement current relate to capacitors?

Displacement current is a fundamental concept in electromagnetism, particularly relevant to capacitors. In a charging or discharging capacitor, there's no actual flow of charges through the dielectric. However, the changing electric field between the plates creates a displacement current. This current is equivalent to the rate of change of electric flux and allows for the continuity of current in AC circuits containing capacitors. It's crucial for understanding how capacitors work in alternating current situations.

34. What is the relationship between capacitance and impedance in AC circuits?

In AC circuits, capacitors exhibit capacitive reactance (Xc), which contributes to impedance:

35. How does the electric field inside a capacitor relate to its stored energy?

The electric field inside a capacitor is directly related to its stored energy:

36. What is the difference between lumped and distributed capacitance?

Lumped vs. distributed capacitance:

37. How do ceramic capacitors compare to film capacitors in terms of performance and applications?

Ceramic vs. Film Capacitors:

38. How does capacitor impedance change with frequency, and why is this important?

Capacitor impedance changes with frequency in an inverse relationship:

39. How do parasitic elements affect the performance of real-world capacitors?

Parasitic elements in real-world capacitors include: