Fundamentals of Electric Charge, Fields, and Energy

Electric Charge

Electric charge exists in two types: negative (like the electron) and positive (like the proton). It is measured in coulombs (C).

Coulomb's Law

Charges repel if they have the same sign, or attract if they have opposite signs. The force increases with the product of the charges and decreases proportionally to the square of the distance separating them.

Electric Field

A vector field where the direction is defined by the path a positive charge would follow. Its modulus is the ratio of the electric force to the value of the test charge.

Superposition Principle

The vector sum of individual forces and fields acting on any charge in the proximity of others.

Field Lines

The path followed by a positive charge located in a field. These open lines originate from positive charges (or infinity) and terminate at negative charges (or infinity).

Potential Difference

The ratio between the work performed by or on a charge and the value of that charge.

Superposition Principle of Potential

The algebraic sum of the individual potentials created by each charge.

Electric Potential

The potential energy per unit of positive charge: V = Ep / q.

Work

The transformation or transfer of energy that occurs when a force causes a displacement.

• The work of friction, which is always negative, is the product of the friction force and the distance traveled.

Power

A measure of the rate at which energy is transferred or work is performed.

Energy

The amount of energy a body possesses is a measure of its ability to produce work.

Kinetic Energy

The energy a body possesses due to its movement, specifically its speed and mass: Ec = 1/2mv².

Potential Energy

The energy a body possesses due to its position. Types include:

• Gravitational: Near the Earth's surface or between any two masses.
• Elastic: Stored in springs.
• Electric: Due to the force of a charge in the proximity of other charges.
• Others.

Theorem of Living Forces

The work done by a force on a body that results in a change in its state of motion is equal to the change in its kinetic energy.