Difference Between Capacitor and Capacitance with Examples and Formulas
A capacitor is an essential passive component in Physics that stores electrical energy in the form of an electric charge on its plates. It consists of two or more conductive plates separated by an insulating material called a dielectric.
The plates may be flat, cylindrical, or spherical, depending on the capacitorβs application. When a voltage source is connected to the capacitor, electrons accumulate on one plate and leave the other, building up a potential difference across the plates.
The dielectric insulator between the plates blocks direct current (DC) while allowing a voltage to appear across the plates. In an alternating current (AC) circuit, the current seems to pass through the capacitor due to regular charging and discharging. This unique property is why capacitors are widely used in circuits for filtering, timing, and energy storage.
Capacitance and Its Formula
The ability of a capacitor to store electrical charge is called capacitance. It is measured as the amount of charge a capacitor can store per unit voltage. The unit of capacitance is the Farad (F), named after Michael Faraday. One Farad is the capacitance when one coulomb of charge is stored with a potential difference of one volt.
The relationship is given by the formula:
C = Q / V
Where C is capacitance (in Farads), Q is charge (in coulombs), and V is voltage (in volts).
Standard Units of Capacitance
| Unit | Symbol | Equivalent in Farads |
|---|---|---|
| Microfarad | ΞΌF | 10-6 F |
| Nanofarad | nF | 10-9 F |
| Picofarad | pF | 10-12 F |
Capacitance of Parallel Plate Capacitor
The capacitance depends on several physical factors: surface area of the plates (A), separation distance (d), and the permittivity of the dielectric material (Ξ΅). The formula for a parallel plate capacitor is:
C = Ξ΅ Γ (A / d)
Where C is capacitance, A is the area of one plate, d is the distance between plates, and Ξ΅ is the absolute permittivity of the dielectric (Ξ΅ = Ξ΅0 Γ Ξ΅r; Ξ΅0 is permittivity of free space, Ξ΅r is relative permittivity).
Example β Capacitance Calculation
Suppose two metal plates of size 30 cm Γ 50 cm are separated by 6 mm air gap. To calculate capacitance:
| Given | Value |
|---|---|
| Area (A) | 0.3 m Γ 0.5 m = 0.15 m2 |
| Distance (d) | 0.006 m |
| Permittivity (Ξ΅0) | 8.854 Γ 10-12 F/m |
| Capacitance | C = Ξ΅0 Γ (A/d) = 8.854 Γ 10-12 Γ (0.15/0.006) = 2.21 Γ 10-10 F = 221 pF |
Factors Affecting Capacitance
| Factor | Effect |
|---|---|
| Plate Area (A) | Larger area increases capacitance |
| Separation Distance (d) | Smaller distance increases capacitance |
| Dielectric Permittivity (Ξ΅) | Higher permittivity increases capacitance |
Role and Advantages of the Dielectric
The dielectric not only insulates but also increases mechanical support and enhances capacitance by a factor called the dielectric constant. Different materials have different dielectric constants.
For example, air, paper, mica, glass, plastic, and ceramics are commonly used as dielectric materials in various capacitor types.
A higher dielectric constant means the capacitor can store more charge for the same plate area and separation. It also allows capacitors to be smaller and withstand higher working voltages.
Types of Capacitors
| Type | Main Features |
|---|---|
| Parallel Plate | Simple construction, used for basic experiments (Learn More) |
| Cylindrical | Coaxial cylinders, often used in cables |
| Spherical | Two concentric spheres, specialized use |
| Multi-plate | More plates increase effective area, higher capacitance |
Step-by-Step Approach to Problem Solving
- Identify all given values (area, distance, voltage, charge, dielectric type).
- Select the relevant formula (e.g., C = Q/V, C = Ξ΅A/d).
- Substitute values with units into the formula.
- Calculate to find the unknown (capacitance, voltage, or charge).
- Check units and reasonability of your answer.
Key Formulas in Context
| Formula | Application |
|---|---|
| C = Q / V | General definition of capacitance |
| C = Ξ΅A / d | Capacitance of a parallel plate capacitor |
| E = (1/2) C V2 | Energy stored in a capacitor (Detailed Guide) |
Practical Applications
- Energy storage and release in electronic circuits
- Blocking DC while allowing AC (Explore More)
- Tuning circuits, filters, and signal processing
- Timing operations in oscillators and timers
Practice Questions
- A capacitor with 10 ΞΌF capacitance carries a charge of 30 ΞΌC. What is the voltage across its plates?
- How will capacitance change if the plate separation is halved while the area and dielectric remain the same?
- Name two practical uses of capacitors in everyday electronic devices.
Further Learning and Resources
- Effect of Dielectric on Capacitance
- Understanding Dielectric Materials
- Charging by Induction β Concept
For a deeper understanding, continue exploring related topics on Vedantu Physics and practise regularly to master the concepts of capacitors, capacitance, and their applications in real-world circuits.
FAQs on Capacitor and Capacitance Explained for Class 12, JEE & NEET
1. What is a capacitor in physics?
A capacitor is an electronic device that stores electrical energy in an electric field. It consists of two conducting plates separated by an insulating material called the dielectric. When a voltage is applied across the plates, charge accumulates, storing energy for later use in circuits.
2. What is capacitance?
Capacitance is the ability of a capacitor to store electric charge per unit voltage across its plates. The SI unit of capacitance is the farad (F). Capacitance indicates how much charge (Q) can be stored at a certain voltage (V), given by the formula: C = Q/V.
3. What is the difference between a capacitor and capacitance?
Capacitor is a physical device, while capacitance is its property.
- Capacitor: A device that stores electrical energy, made of two conductors separated by an insulator.
- Capacitance: The ability to store charge per unit voltage, measured in farads (F).
4. What is the SI unit of capacitance?
The SI unit of capacitance is the farad (F).
One farad is defined as the capacitance when one coulomb of charge stored produces a potential difference of one volt across the plates.
5. What is the formula for the capacitance of a parallel plate capacitor?
The capacitance of a parallel plate capacitor is given by:
C = (πβ Γ A) / d
where:
- πβ = Permittivity of free space (8.85 Γ 10β»ΒΉΒ² F/m)
- A = Area of one plate (mΒ²)
- d = Distance between plates (m)
6. What is the energy stored in a capacitor?
The energy (E) stored in a capacitor is calculated by:
E = (1/2) C V2
where C is the capacitance in farads and V is the voltage applied across the capacitor in volts. The energy is measured in joules (J).
7. How does the dielectric material affect the capacitance of a capacitor?
A dielectric material increases the capacitance of a capacitor.
It allows the plates to store more charge for the same voltage by increasing the effective permittivity. The greater the dielectric constant (k), the higher the capacitance.
- New capacitance: C = (k Γ πβ Γ A)/d
8. What are the main uses of capacitors in circuits?
Capacitors are widely used in electrical and electronic circuits for:
- Storing and releasing energy
- Filtering noise in power supplies
- Smoothing voltage fluctuations
- Tuning radios and TV circuits
- Timing applications and oscillators
9. How does a capacitor charge and discharge in a circuit?
A capacitor charges by accumulating electrons on one plate and positive charge on the other when connected to a voltage source.
Discharging occurs when the stored energy is released through a connected load or circuit.
Charging and discharging follow exponential laws; the rate is controlled by the circuit's resistance and capacitance (RC time constant).
10. What happens if the voltage across a capacitor exceeds its rated value?
If the applied voltage exceeds the rated value, the dielectric material can break down, causing:
- Permanent damage to the capacitor
- Possible short circuit or failure
- Loss of insulation property and leakage
11. How can you calculate the total capacitance for capacitors connected in series and parallel?
For capacitors in parallel:
Ctotal = C1 + C2 + ... + Cn
For capacitors in series:
1/Ctotal = 1/C1 + 1/C2 + ... + 1/Cn
Parallel increases total capacitance, while series decreases it.
12. What are the different types of capacitors?
The main types of capacitors are:
- Parallel plate capacitor
- Cylindrical capacitor
- Spherical capacitor
- Variable capacitor
- Ceramic, electrolytic, film, and mica capacitors (based on dielectric)
