Electromagnetism

Electromagnetism is a fascinating interaction that happens between tiny parts of matter called particles that have something called an electric charge. This interaction happens through special fields known as electromagnetic fields. Electromagnetism is one of the four main forces in nature and it plays a big role in how atoms and molecules behave.

You can think of electromagnetism as a mix of two things: static electricity, like the shock you feel when you touch a doorknob after walking on carpet, and magnetism, like the force from a magnet. These two forces are different but very closely connected. Charged particles can attract or push away from each other depending on their charges, and when they move, they create magnetic effects. These ideas are described using special 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 the molecules that make up all living things, 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 very 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 create mathematical ways 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 using modern ideas from physics, which helps us understand 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 these things happened.

In the 1800s, scientists learned that electricity and magnetism were connected. James Clerk Maxwell showed that electric charges and magnetic poles pull toward or push away from each other, depending on whether they are alike or different. He also discovered 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 are important for how atoms and molecules work together. They explain why materials have certain properties 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 noticed that lightning could change the direction of a compass needle. Scientists later discovered that electricity and magnetism are connected. In the 1800s, a scientist named James Clerk Maxwell brought together many ideas about electricity and magnetism into one theory. He showed that light is a kind of wave made of electricity and magnetism.

Maxwell’s work helped explain how electricity and magnetism work together. Even though it was hard to fit with older science ideas, Albert Einstein later showed how it all made sense with his theory of special relativity. Today, scientists still have some questions about electromagnetism, like why certain natural things can sense electric and magnetic fields.

Extension to nonlinear phenomena

The Maxwell equations are straightforward because a change in electric charges or currents causes a matching change in the electromagnetic fields. However, more complex behavior can happen when electromagnetic fields interact with materials that have their own complex rules. This is explored in areas like magnetohydrodynamics, which mixes Maxwell’s ideas with the movement of fluids, and nonlinear optics, which studies how light behaves 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 that make calculations look different from the more common SI system.

Applications

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