Capacitor and Capacitance: Definition, Formulas, Types, Applicatuons & Class 12 Notes

A capacitor is an electronic device used to store electric charges. It consists of two conductive plates placed at a distance. The gap between the conductor plates is filled with dielectric. A dielectric is an insulating material that opposes the flow of charges. When current is passed through the capacitor, one plate becomes positive and the other negative.  This creates an electric field in the dielectric,

potential energy. 

We know that a capacitor is an electrical component that is used to store electric charges in the form of electric potential energy.

Before studying the working of a capacitor, it is important to know its components for better understanding. Above, in the definition of a capacitor, it is already explained that a capacitor consists of two conductive plates. These plates are placed at a distance. The gap between the plates is filled by dielectric material such as glass, plastic, air, etc. 

When a power source is applied to the capacitor, one plate becomes positive charge and the other negative charge. Due to the dielectric material, the electric field formed between the plates is stored as potential energy. This energy is stored until the voltage across the capacitor becomes equal to the voltage of the battery. The energy stored between the plates is released when the capacitor is discharged.

 

We can express the capacitance as the ability of a capacitor to store electric charge per unit voltage.  In practical circuits, capacitance is measured in picofarads (pF), nanofarads (nF),  or microfarads (µF). 

Also Read: NCERT Solution for Class 11 & 12

The capacitance of a capacitor is affected by:  

1. Area (A): Capacitance is directly proportional to the area. The larger the area, the higher the capacitance value.  

2. Distance (d): The capacitance is inversely proportional to the distance between the plates. The smaller the distance, the higher the capacitance value. 

3. Dielectric constant (ε): The Higher the permittivity space higher the capacitance.

Formula for parallel plate capacitor: 

$C=\frac{{\epsilon }_0{\epsilon }_{r}A}{d}$

Where, 

• permittivity of free space - ε0​.
• Relative permittivity (dielectric constant) - εr​.

Capacitors can be connected in series and parallel:

Capacitor in Series

Capacitors are connected end to end; therefore, the same charge flows through each capacitor.

Formula: $\frac{1}{C_{eq}}=\frac{1}{C_1}+\frac{1}{C_2}+\frac{1}{C_3}+...$

Key points:

1. In a series connection total capacitance decreases.

2. Voltage is divided among the capacitors.

3. Used when a lower overall capacitance is required.

Capacitor in Parallel

All capacitors are connected across the same two points; thus, the voltage is the same across the capacitors.

Formula: $C_{eq}=C_1+C_2+C_3+...$

Key Points:

1. Total capacitance increases

2. Charge division among the capacitors.

3. Used when a high overall capacitance is required

 

The capacitor is classified as: 

1. Ceramic capacitors
2. Tantalum capacitors
3. Film capacitors
4. Electrolytic capacitors

Important Links:

NCERT Class 11 notes	Class 11 Physics NCERT notes
Chemistry Class 11 notes	NCERT Class 11 Maths notes

The energy stored in a capacitor is given as

$U=\frac{1}{2}C{V}^2$

The capacitor stores the energy in the electric field of the dielectric.