Electric Charge Explained: Properties, Types, and Coulomb's Law
Electric charge is a cornerstone of physics, explaining everything from static cling to the electricity that powers our homes. This guide breaks down the essential concepts of electric charge, its fundamental properties, and the law that governs its interactions.
What is Electric Charge?
Definition: Electric charge is a basic, fundamental property of matter that causes it to experience a force when placed in an electromagnetic field. In simpler terms, it's the property responsible for all electric forces.
The Two Types of Electric Charge
All electric charges are one of two types:
- Positive Charge (+): This type of charge is carried by protons, which are subatomic particles found in the nucleus of an atom.
- Negative Charge (−): This type of charge is carried by electrons, the subatomic particles that orbit the nucleus of an atom.
The interaction between these charges is the basis of electricity. As the image illustrates, opposite charges attract each other (a positive and negative charge will pull together), while like charges repel each other (two positive charges or two negative charges will push apart).
Fundamental Properties of Electric Charge
Electric charge has several key properties that are universally true:
- Conservation of Charge: Charge is never created or destroyed; it is only transferred from one object to another. The total electric charge in an isolated system remains constant.
- Quantization of Charge: Electric charge exists in discrete, indivisible units. This smallest unit of charge is known as the elementary charge, which is the magnitude of charge on a single electron or proton (approximately ±1.6 x 10⁻¹⁹ C). Any observable charge is an integer multiple of this elementary charge.
- Additivity of Charge: The total charge of a system is simply the algebraic sum of all the individual charges present in it. For example, if a system contains a +3 charge and a -1 charge, the total charge is +2.
Coulomb's Law: The Force Between Charges
The interaction (attraction or repulsion) between charges can be quantified using Coulomb's Law.
- Describes: Coulomb's Law calculates the magnitude of the electric force between two stationary point charges.
- Force Type: The force can be attractive (between opposite charges) or repulsive (between like charges).
- Formula: The formula for Coulomb's Law is:
*F = k |q₁ · q₂| / r²**
Where:
- F is the electric force.
- k is Coulomb's constant, approximately 8.99 × 10⁹ N·m²/C².
- q₁ and q₂ are the magnitudes of the two charges.
- r is the distance between the centers of the two charges.
The diagram of the electric field between a positive and negative charge (an electric dipole) visually represents this force, with field lines originating from the positive charge and terminating on the negative charge, showing the path a positive test charge would take.
Units of Electric Charge
- SI Unit: The standard unit of electric charge is the Coulomb (C).
- Electron Charge: The charge of a single electron is -1.6 x 10⁻¹⁹ C.
- Coulomb in Terms of Electrons: One Coulomb is equivalent to the total charge of approximately 6.25 x 10¹⁸ electrons.
