A SIMPLE CAPACITANCE CALCULATOR

This calculator can be used to calculate the capacitance of a capacitor, series capacitance, and parallel capacitance.

What is capacitance?

Capacitance is a measure of the capacitor’s ability to store charge.

Capacitors are devices used to store large amounts of electrical energy. A capacitor consists of two conducting surfaces (usually metal plates) separated by an insulating material such as air, or paper. The insulating material is called dielectric.

SI unit of capacitance

The SI unit of capacitance is Farad.

The sub-units of Farad are:

1. Kilofarad
2. Milifarad
3. Microfarad
4. Nanofarad
5. Picofarad

Example:

Convert the following values:

1. 0.5µF to nF

1×10³ µF = 1nF

0.5 x 10³= 500nF

2. 600pF to µF

1 ×10^-6pF = 1µF

600 × (1×10^-6) = 0.0006µF

3. 22nF to F

1×10^-9 nF = 1F

22 × (1×10^-9) = 0.000000022F

Capacitance Formula

The basic equation for capacitance is:

 C=Q/V 

Where 

C=Capacitance in Farads

Q=Charge held on plates in coulombs

V=Potential difference across plates in Volts

To be able to remember the formula easily we can use the capacitance memory triangle.

(Image source: electronics-tutorials)

From the memory triangle above we can come up with three equations:

(Image source: Electronicnotes)

Capacitor Symbol

In a diagram, capacitance is expressed by the image below:

Parallel Capacitance

(Image source:Lambdageeks.com)

To calculate capacitors in parallel use the equation:

C_n=C₁+C₂+C₃

EXAMPLE

Calculate the total capacitance in the circuit above where C1=12F, C2=20F, and C3=2F

C_n=C₁+C₂+C₃

C=12F+20F+2F

=34F

Series Capacitance

(Image source:electrical4u.com)

The formula is:

1/C_n=1/C₁+1/C₂+1/C₃

Calculate the total capacitance in the circuit above where C1=21F, C2=10F, and C3=12F

1/C_n=1/21+1/10+1/12

1/C_n=97/420

C_n=4.33F

Factors that affect Capacitance

• AREA OF PLATES

Capacitance is directly proportional to the plate area. The larger the plate area, the greater the capacitance, and the smaller the plate the less the capacitance.

• DIELECTRIC MATERIAL

All other factors being equal, the greater the dielectric constant(K) the greater the capacitance, and the less the dielectric constant(K) the less the capacitance.

• PLATE SEPARATION DISTANCE

All other factors being equal, the greater the distance the less the capacitance, and the less the distance the greater the capacitance. This is because capacitance is directly proportional to the electrostatic force field between the plates and the field is stronger when the plates are closer together. 

In summary, capacitance is affected by:

1. Area of plates
2. Separation distance
3. Dielectric material

FORMULA:        

C=εA/d 

where

          C=capacitance in farads

          A=Area of plate overlap

          ε=permittivity of dielectric

          D=distance between plates in meters

(Image source:slideplayer.com)

Example

A capacitor is constructed from two conductive metal plates 30cm x 50cm which are spaced 6mm apart from each other and uses dry air as its only dielectric material. Calculate the capacitance of the capacitor.(ε=8.854x10^-12)

C=εA/d

A=0.3 x 0.5 m²

d=6 x10^-3m

C=8.854x10^-12X(0.3x0.5)/(6x10^-3)

=0.221nF

REFERENCES

• Factors affecting capacitance| Dielectric constant. Electric Academia. https://electricalacademia.com/basic-electrical/factors-affecting-capacitance/
• Fowler (2003). Electricity Principles and Applications. SlidePlayer. https://slideplayer.com/slide/15391692/
• Factors affecting capacitance. All about circuits. https://www.allaboutcircuits.com/textbook/direct-current/chpt-13/factors-affecting-capacitance/
• Introduction to capacitors. Electronics tutorials. https://www.electronics-tutorials.ws/capacitor/cap_1.html
• Capacitance(PDF). http://www.phys.ufl.edu/courses/phy2054/s09/lectures/2054_ch16B.pdf
• Capacitors formulas. Electronics notes. https://www.electronics-notes.com/articles/basic_concepts/capacitance/capacitor-formulas-equations.php