Electric Charges, Fields, and Potentials: A Comprehensive Overview
Electric Charge and Coulomb’s Law
Electric Charge
Electric charge is a fundamental property of matter, similar to mass. There are two types of charges: positive and negative. A body is positively charged when it has a deficit of electrons and negatively charged when it has an excess of electrons. Electric charge is a scalar quantity measured in Coulombs (C). The elementary charge, the charge of a single electron or proton, is approximately 1.6 x 10-19 C. A collection of 6.25 x 1018 electrons represents one Coulomb of charge.
Coulomb’s Law
Coulomb’s Law quantifies the force between two electric charges. This force is directly proportional to the product of the charges and inversely proportional to the square of the distance between them. Mathematically, it’s similar to Newton’s Law of Universal Gravitation, but with key differences: electrical forces can be attractive or repulsive, and the constant of proportionality (K) depends on the medium in which the charges reside.
Electric Fields and Potential
Concept of Electric Field
An electric field exists in a region of space if a charge placed in that region experiences a force. The electric field strength (E) is defined as the force per unit charge.
Electric Potential Energy
Like gravitational force, the electric force is conservative, allowing for the definition of electric potential energy. The work done by the electric force between two points is equal to the negative change in potential energy between those points.
Lines of Force (Electric Field Lines)
Electric field lines are imaginary lines that illustrate the path a positive test charge would follow in an electric field. They originate from positive charges and terminate on negative charges. The density of these lines represents the field strength.
Field Intensity
Field intensity is the number of field lines passing through a unit area perpendicular to the lines. In a uniform electric field, the field lines are parallel, and the field strength is constant.
Electric Flux and Gauss’s Theorem
Electric flux measures the number of field lines passing through a given surface. Gauss’s theorem relates the electric flux through a closed surface to the net charge enclosed within that surface.
Electric Potential (V)
Electric potential (V) at a point is defined as the potential energy per unit positive charge at that point. It’s measured in volts (V), equivalent to joules per coulomb (J/C).
Electron Volt
One electron volt (eV) is the work required to move an electron through a potential difference of one volt.
Equipotential Surfaces
Equipotential surfaces are surfaces of constant electric potential. No work is done when moving a charge along an equipotential surface. The electric field is always perpendicular to equipotential surfaces.
Magnetic Fields
Introduction to Magnetic Fields
Magnetic fields are created by magnets and moving charges. The magnetic field is characterized by the magnetic induction vector (B).
Action of a Magnetic Field on a Moving Charge
A moving charge in a magnetic field experiences a force perpendicular to both its velocity and the magnetic field direction. This force causes the charge to follow a curved path without changing its speed.