Effect of Dielectric on Capacitance: Definition, Formula, Applications & Class 12 Notes

A dielectric is an insulating material placed between the plates of a capacitor. Examples of dielectrics include air, glass, plastic, paper, and ceramics. Dielectric affects the electric field between the plates, thus influencing the capacitance.

After the introduction of a dielectric between the plates of the capacitor: 

1. Dielectric reduces the effect of the electric field.
2. Less voltage is required for the same amount of charge across the plates.
3. This increases the capacitance.

Also Read: 

NCERT Class 11 notes	Class 11 Physics NCERT notes
NCER Class 11 Chemistry notes	Maths Class 11 NCERT Notes

Capacitance increases due to various reasons such as polarization, reduced electric field, decreased voltage and increased capacitance. Let's discuss these factors below.

• Polarization: The dielectric material reduces the effective electric field between the plates. This happens because the molecules between the plates get polarized.
• Decrease Voltage: Dielectric reduces the potential difference (voltage) between the plates for the same amount of charge.
• Increase Capacitance: If the potential difference (V) of the same charge is decreased, the capacitance increases.

The material's ability to store electrical energy in an electric field is measured through the dielectric constant. It is also referred to as relative permittivity.

Formula of dielectric constant: 

${\epsilon }_r=\frac{C}{C_0}$

Where,

• Dielectric Constant is $\varepsilon_r$
• Capacitance with dielectric is C.
• Capacitance without a dielectric is $C_0$ .

Capacitance with a parallel plate capacitor with a dielectric is expressed as:

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

Where,

• C is capacitance.
• $\varepsilon_0$
• $\varepsilon_r$
• d is the distance between the plates.
• A is the area of a plate.

 

1.  Capacitors in Electronic Devices

• Dielectric increases the capacitance without requiring larger plates or closer spacing. 
• Compact high-capacitance capacitors are used in power supplies, radios, mobiles and computers. 

2. Energy Storage Systems

• Capacitors can store more energy in a small space due to dielectrics. 
• Supercapacitors with high-dielectric materials store and release energy quickly. 

3. Insulation in High Voltage Equipment's

• Due to their excellent electrical insulating properties, dielectrics are used in power cables, transformers, and circuit breakers. 

4. Dielectric Heating (Industrial and Medical)

• Used in a microwave (for heating). 
• Industrial drying of foods, textiles, and wood. 
• Medical diathermy for deep tissue heating in physiotherapy. 

5. Sensors and Touch-Sensitive Devices

• Used in capacitive sensors: 
• Dielectric is used in proximity sensors, liquid level detectors, and proximity sensors

Students can find here the link for NCERT Class 12 Physics notes.

Sl. No	Name of Chapter
1	Chapter 1: Electric Charges and Fields
2	Chapter 2: Electrostatic Potential and Capacitance
3	Chapter 3: Current Electricity
4	Chapter 4: Moving Charges and Magnetism
5	Chapter 5: Magnetism and Matter
6	Chapter 6: Electromagnetic Induction
7	Chapter 7: Alternating Current
8	Chapter 8: Electromagnetic Waves
9	Chapter 9: Ray Optics and Optical Instruments
10	Chapter 10: Wave Optics
11	Chapter 11: Dual Nature of Radiation and Matter
12	Chapter 12: Atoms
13	Chapter 13: Nuclei
14	Chapter 14: Semiconductor Electronics: Materials, Devices and Simple Circuits