Electromagnetism

Electromagnetism is a special interaction between tiny parts of matter called particles that have an electric charge. This interaction happens through fields called electromagnetic fields. Electromagnetism is one of the four main forces in nature. It helps atoms and molecules behave the way they do.

You can think of electromagnetism as a mix of two things: static electricity, like the shock you feel when you touch a doorknob, and magnetism, like the force from a magnet. These two forces are different but closely connected. Charged particles can attract or push away from each other, and when they move, they create magnetic effects. These ideas are described using laws like Coulomb's law for electricity and Ampère's force law for magnetism.

Electromagnetism is very important in our everyday lives. It helps hold atoms together, allows atoms to combine and form molecules, and is behind many modern technologies. This includes how we produce and use electricity, how we see light, how we send messages wirelessly, and how many machines work.

People have been curious about electromagnetism for a long time. Ancient groups like the Greeks and the Mayans tried to explain things like lightning and magnets. But it wasn’t until the late 1700s and 1800s that scientists like Gauss and Faraday started to understand it better. In the 1860s, a scientist named Maxwell created important equations that showed how electricity and magnetism are connected and predicted that light is a type of wave.

Today, scientists continue to study electromagnetism to learn more about how the world works.

History

Main article: History of electromagnetic theory

People have noticed strange forces in nature for thousands of years. Ancient Chinese, Mayan, and Egyptian cultures knew that a special rock called magnetite could pull on other objects. They also saw lightning and felt static electricity from rubbing things together, but they didn’t understand why.

In the 1800s, scientists learned that electricity and magnetism were connected. James Clerk Maxwell showed that electric charges and magnetic poles can pull together or push apart. He found that electric currents create magnetic fields and that moving a magnet near a wire can create an electric current. These discoveries helped us understand that light and other waves, like radio waves and gamma rays, are all forms of electromagnetic energy.

A fundamental force

The electromagnetic force is one of the four main forces in nature and is very strong. It works over any distance. Many everyday forces, like friction or the push and pull you feel when you touch objects, come from this electromagnetic force.

Electromagnetic forces help atoms and molecules stick together. They explain why materials act the way they do and how chemical reactions happen. When you push or pull something, it's really the tiny particles inside those objects interacting through electromagnetic forces.

Classical electrodynamics

Main article: Classical electrodynamics

Long ago, people saw that lightning could move a compass needle. Scientists found out that electricity and magnetism are linked. In the 1800s, a scientist named James Clerk Maxwell combined many ideas about electricity and magnetism into one theory. He showed that light is a wave made of electricity and magnetism.

Maxwell’s work helped explain how electricity and magnetism work together. Later, Albert Einstein showed how this fits with his theory of special relativity. Today, scientists still have questions about electromagnetism.

Extension to nonlinear phenomena

The Maxwell equations are simple because a change in electric charges or currents causes a matching change in the electromagnetic fields. But more complex behavior can happen when electromagnetic fields interact with special materials. This is studied in areas like magnetohydrodynamics, which mixes Maxwell’s ideas with fluid movement, and nonlinear optics, which looks at how light acts in special materials.

Quantities and units

See also: List of physical quantities and List of electromagnetism equations

Here are some important units used when studying electromagnetism:

• ampere (electric current, SI unit)
• coulomb (electric charge)
• farad (capacitance)
• henry (inductance)
• ohm (resistance)
• siemens (conductance)
• tesla (magnetic flux density)
• volt (electric potential)
• watt (power)
• weber (magnetic flux)

Different systems of units can change how these quantities are used in equations. Some systems, like CGS, have special rules.

Applications

The ideas behind electromagnetism help us make things like electric circuits, magnetic circuits, and semiconductor devices. These tools are important in many technologies we use every day.