Classical electromagnetism

Tiny bits of power move in ways that push and pull. This is called electricity and magnetism. Scientists study how these two things work together.

When power moves, it can make waves. These waves travel through space. Some waves are radio waves. Other waves are light.

Light travels very fast. It moves at the speed of light. These waves can even be x-rays.

Moving power can also push on small bits. This push is a special force. It helps us understand how the world works. It is a very big and cool idea.

Scientists study how electric charges and currents work together. This study is called classical electromagnetism. It looks at how these charges push and pull on each other.

One important part is the electric field. This is a field that can push on a charge. We can also measure the electric potential. This is often called voltage. It helps us understand how much power is in a spot.

When these fields change, they make waves. These waves move away from where they started. They can travel through a vacuum, which is empty space. These waves move at the speed of light. There are many kinds of these waves. Radio waves and microwaves are two examples. Light is also a wave. Other waves include x-rays and gamma rays.

There is also a special force called the Lorentz force. This force acts on particles that have a charge. It is made of two parts. One part comes from the electric field. The other part comes from the magnetic field. Together, they push the particle in a new direction. This helps us understand how electricity and magnetism work as one big system.

Classical electromagnetism is a very important part of physics. It is the study of how electric charges and currents interact. These interactions happen through things called fields. Scientists use this theory to describe how electricity and magnetism work together. This works best when things are not too tiny. When we look at very small distances, we use a different theory called quantum electrodynamics. But for most of our world, classical electromagnetism is the right tool.

One way these charges work is through the Lorentz force. This force acts on particles that have a charge. It is actually made of two different parts. One part comes from the electric field. The other part comes from the magnetic field. The magnetic part is special because it pushes the particle in a direction perpendicular to its motion. When you add these two parts together, you get the total Lorentz force. This shows how the two fields act as one system.

People have studied these forces for a very long time. In the past, people studied light and electricity as separate things. This changed because of the work of Michael Faraday. He did experiments that suggested an electromagnetic field exists. Later, James Clerk Maxwell used math to describe it all. He wrote a famous book in 1873 called A Treatise on Electricity and Magnetism. His work helped us understand how these fields work together.

There are many specific facts and numbers in this science. We can measure the electric field in volts per meter. We also use the term voltage to talk about electric potential. Scientists use many different tools to measure things like current and resistance. We can even see these forces in action through electromagnetic waves. These waves include radio waves, microwaves, and visible light. They also include x-rays and gamma rays. All these waves travel at the speed of light.

This science connects to many things you use every day. It is the basis for electrical and electronic engineering. Engineers use models to understand how things like wires and antennas work. They also study how light moves through lenses and mirrors. Even the parts inside a computer, like integrated circuits, rely on these rules. From the radio in a car to the light in a room, electromagnetism is everywhere. It helps us build the technology that runs our world.

Classical electromagnetism, also called classical electrodynamics, is a major branch of physics. It focuses on the study of how electric charges and currents interact with one another. This field of study uses an extension of the classical Newtonian model of physics. Because of this, scientists call it a classical field theory. This theory describes electromagnetic phenomena when the length scales and field strengths are large. In these cases, quantum mechanical effects are negligible and do not interfere with the results. However, when looking at very small distances or low field strengths, scientists use quantum electrodynamics instead. That is a quantum field theory used for much smaller scales.

The way these fields act on particles is described by the Lorentz force. This force acts on any particle that carries an electric charge. The Lorentz force is actually the sum of two different vectors. The first part is the force from the electric field at the particle's location. The second part is a magnetic force. This magnetic part is calculated using the cross product of the particle's velocity and the magnetic field. Because of how cross products work, this force pushes the particle perpendicularly to both its velocity and the magnetic field. The total force is the combination of these two distinct movements.

An electric field, or E, is defined by how it acts on a stationary test charge. If you place a small test charge, known as q0, in a field, the field is the force on that charge divided by the charge itself. The unit for the electric field is newtons per coulomb, or N/C. This is also equal to volts per meter, or V/m. In the study of electrostatics, charges are not moving. In these cases, the forces from many different point charges can be summed together. This uses Coulomb's law to find the total force at a specific position. If the charges are spread out in a continuous distribution, scientists use an integral to calculate the field.

To make these complex calculations easier, scientists use a concept called electric potential. This is also commonly known as voltage. The unit of measurement for electric potential is the volt. The electric field can be understood as the negative gradient of this potential. This means the electric field is essentially the change in potential over a distance. While the scalar potential is very helpful for breaking down complex problems, it is not always enough on its own. According to Maxwell's equations, a correction factor is sometimes needed. This is done by subtracting the time derivative of the vector potential. This is especially true when charges are not moving in a steady, or quasistatic, way.

History shows that people studied electricity and magnetism as separate topics for a very long time. For example, the field of optics was studied for centuries before anyone knew light was an electromagnetic wave. The modern understanding of electromagnetism grew from the work of Michael Faraday. His experiments suggested that an electromagnetic field actually exists. Later, James Clerk Maxwell used differential equations to describe these fields. He published his findings in 1873 in a book called A Treatise on Electricity and Magnetism. This work helped develop methods to measure voltage, current, capacitance, and resistance.

A changing electromagnetic field will eventually propagate away from its source as a wave. These electromagnetic waves travel through a vacuum at the speed of light. They exist across a wide spectrum of different wavelengths and frequencies. The spectrum includes radio waves and microwaves at lower frequencies. It also includes light, which consists of infrared, visible, and ultraviolet rays. At the highest frequencies, the spectrum contains x-rays and gamma rays. In the field of particle physics, this radiation is seen as the manifestation of the electromagnetic interaction between charged particles.

Classical electromagnetism is vital for many different models and engineering fields. It provides the foundation for electrical and electronic engineering. Engineers use specific models to understand things like moving point charges or electric currents in a conductor. They also study transmission media, such as wires, antennas, and waveguides. Other models focus on how light moves through mirrors or lenses. Even modern technology, like integrated circuits, relies on these electromagnetic principles. By using these mathematical models, scientists can understand everything from a simple resistor to a complex computer chip.