Electricity and Magnetism

Learning Objectives

Describe electric charge and the principles of electrostatics (like charges repel, opposite charges attract).

Define electric current, voltage, and resistance, and relate them using Ohm's Law (V=IR).

Explain that moving electric charges (currents) produce magnetic fields.

Describe how a changing magnetic field can induce an electric current (electromagnetic induction).

The Two Faces of a Single Force

Electricity and magnetism were once thought to be separate phenomena, but they are deeply intertwined aspects of a single fundamental force: electromagnetism.

Electricity

Electric Charge: A fundamental property of matter that can be positive or negative. Protons have a positive charge, and electrons have a negative charge.

Electrostatics: The study of stationary charges. The core principle is that like charges repel and opposite charges attract.

Electric Current (I): The rate of flow of electric charge. It is measured in Amperes (A).

Voltage (V): Also known as potential difference, it is the 'electrical pressure' or work per unit charge that drives current flow. It is measured in Volts (V).

Resistance (R): A measure of the opposition to current flow. It is measured in Ohms (Ω).

Ohm's Law describes the relationship between these three quantities for many materials:

V = IR

Magnetism

Magnets have a north pole and a south pole. Like poles repel, and opposite poles attract.

Unlike electric charges, magnetic poles cannot be isolated; you can't have a 'monopole'. If you cut a magnet in half, you get two smaller magnets, each with a north and south pole.

Magnets create magnetic fields, which are vector fields that describe the magnetic influence on moving electric charges, electric currents, and magnetic materials.

The Connection: Electromagnetism

1.Moving Charges Create Magnetic Fields:

A wire carrying an electric current produces a circular magnetic field around it. This is the principle behind electromagnets. The direction of the field can be found using the right-hand rule.

2.Changing Magnetic Fields Create Electric Currents:

This is Faraday's Law of Induction. If you move a magnet through a coil of wire, or change the strength of the magnetic field passing through it, a voltage is induced in the coil, which can drive a current.

This is the fundamental principle behind electric generators (which convert mechanical energy into electrical energy) and transformers.

This deep connection shows that electricity and magnetism are two sides of the same coin, unified by James Clerk Maxwell's equations.

Key Terms

Ohm's Law: A law stating that electric current is proportional to voltage and inversely proportional to resistance (V=IR).
Electric Current (I): The rate of flow of electric charge, measured in Amperes (A).
Voltage (V): The electric potential difference between two points, which is defined as the work needed per unit of charge to move a test charge between the two points. Measured in Volts (V).
Resistance (R): A measure of the opposition to current flow in an electrical circuit, measured in Ohms (Ω).
Electromagnetic Induction: The production of an electromotive force (i.e., voltage) across an electrical conductor in a changing magnetic field.