Electrostatics is the branch of physics that studies stationary electric charges and their interactions. Electric charge is a fundamental property of matter, similar to mass. There are two types of electric charge: positive and negative. The basic principle of electrostatics is that like charges repel each other, while opposite charges attract. This was first observed in ancient times when people noticed that rubbing amber with fur could attract small objects, giving us the word electricity from the Greek word elektron, meaning amber.
Coulomb's Law is the fundamental equation that quantifies the electrostatic force between two point charges. The law states that the force is directly proportional to the product of the charges and inversely proportional to the square of the distance between them. The constant k, known as Coulomb's constant, has a value of approximately 8.99 times 10 to the 9th power Newton meters squared per coulomb squared. This inverse square relationship means that doubling the distance reduces the force by a factor of four, while doubling either charge doubles the force.
Electric field is a fundamental concept that describes the influence a charge exerts on the space around it. It is defined as the electric force per unit charge, with the equation E equals F over q. Electric field lines provide a visual representation of the field, showing the direction a positive test charge would move. Field lines always start from positive charges and terminate on negative charges. For a single positive charge, field lines radiate outward in all directions. The density of field lines indicates the strength of the electric field - closer lines mean stronger field.
Electric potential energy represents the energy stored in a system of electric charges due to their positions. For two point charges, the potential energy is given by U equals k times q1 times q2 divided by r, where r is the distance between the charges. This energy changes as charges move within electric fields. The graph shows how potential energy varies with distance for two opposite charges. When opposite charges are far apart, the potential energy is close to zero. As they move closer together, the potential energy becomes more negative, indicating that the system naturally moves toward this lower energy state.
Electric potential is defined as the electric potential energy per unit charge, given by V equals U over q. It represents the work done per unit charge to bring a test charge from infinity to a specific point in an electric field. Equipotential surfaces are imaginary surfaces where every point has the same electric potential. These surfaces are always perpendicular to electric field lines. Around a positive point charge, equipotential surfaces form concentric circles, with higher potential closer to the charge. Positive charges naturally move from regions of high potential to low potential, similar to how objects fall from high to low gravitational potential energy.