# Électrostatique

## What is Electrostatics?

Electrostatics is the study of electric charge which is not moving i.e. it does not move, it is static.

After reading this article, you’ll learn the necessary terms and keywords for the under-listed and you will be able to answer questions on Electrostatics, and the rest of them.

• Electrostatics.
• Charge.
• Coulomb’s law.
• Electric field and
• Capacitors.

### CHARGE

All objects surrounding us (including people) contain a large amount of electric charge. A charge can be negative or positive and it is measured in the unit called coulombs (C). However, objects can either be electrically neutral or electrical charged.

A charge has three important properties which are;

1. A charge is always conserved. Charge, just like energy, cannot be destroyed nor created.
2. The charge comes in discrete packets. The smallest unit of charge is that carried by one electron called the elementary charge, e, and by convention, it has a negative sign (e= -1.6 x 10-19C)
3. Charge object exerts electrostatics forces on each other. Like charges repel and unlike charges attract each other.

There are three (3) ways of charging a neutral body;

1. By Friction: This is the act of rubbing two bodies together so that each of the body losses or gains charge. The one that loses charge becomes positive while the one that gains charge becomes negative.
2. By Contact: Bringing two bodies together.
3. By Induction: The process of bringing two bodies together from far while a charge takes place. Charging by induction requires no contact with the object inducing the charge and the object is left with the opposite charge.
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### COULOMB’S LAW

The behavior of the electrostatic force was studied in detail by Charles Coulomb around 1784. Through his observation, he was able to show that the electrostatic force between two point-like charges situated in a vacuum is inversely proportional to the square of the distance between the objects. He also discovered that the force is proportional to the product of the charges on the two objects.

“Coulomb’s law states that in a given medium, the force of attraction or repulsion “F” between two bodies will charge “Q and q” is directly proportional to the product of the charge and inversely proportional to the square of its distance “r”

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### ELECTRIC FIELD

• Isolated Charge: A charge is said to be isolated when it is standing on its own (either positive or negative charge)

• A line of force for two like charge.

• A line of force for two unlike charged body

### CAPACITORS

These are electrical/electronic devices use in storing charges in the form of electrical energy. There are three (3) major types of capacitors namely;

#### Ceramic Capacitors:

They are small in size and value, ranging from a few Pico Farads to 1 µ Not polarized, so either end can go to the ground. Value is given by a mystical code somewhat like that of resistors.

#### Electrolytic Capacitors:

They look like small cylinders and range in value from 1 µF to several Farads. Very inaccurate and change in value as the electrolytic ages. Polarized, the cathode must go to the ground. A cathode is marked with a minus sign on the case. Value is usually written on the case.

#### Tantalum Capacitors:

They are similar in size to ceramic but can hold more charge, up to several hundred µ Accurate and stable, but relatively expensive. Usually polarized, an anode is marked with a plus sign.

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Other common types of capacitors are Mayer capacitors, Percept/variable capacitors, Paper capacitors, Parallel plates capacitors etc…

#### USES OF CAPACITORS

• To store an electric charge.
• They stabilize voltage and power flow.
• It is used in an electronic circuit as a filter.
• It is used for an oscillating circuit.
• It is used to block noise in a direct current circuit (DC Circuit)

#### FACTORS THAT AFFECTS CAPACITORS

• Effective surface area (C α A)
• The distance between the plate (C α 1/d)
• The presence of a dielectric material (C α ε)
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