The electromagnetic force pushes or pulls anything that has anelectric charge, likeelectrons andprotons. It includes theelectric force, which pushes all charged particles, and themagnetic force, which only pushes moving charges.
There are two types of electric charge: positive and negative. The electric force pulls opposite charges (positive and negative) towards each other. It pushes similar charges (both positive, or both negative) away from each other.[2]
The electromagnetic force comes from something called an electromagnetic field. In physics, a field is how we keep track of things that might change in space and time. It is like a set of labels for every point in space. For instance, the air temperature in a room could be described by a field, where the labels are just numbers saying how hot it is at that point in the room. We could have more complicated labels as well. On a map of wind speeds, the label could be a number saying how strong the wind is and also an arrow saying which way it is blowing. We call this avector field because each label is a vector - it has a direction (the arrow) and a magnitude (its strength).[3]
Electric and magnetic fields are also fields. Instead of keeping track of temperature or wind speed, they tell us how much push or pull acharged particle will feel at that point in space, and which direction it will be pushed. Like wind speeds, electric fields are also vector fields, so they can be drawn as arrows. The arrows point which way a positive particle, like aproton, will be pushed if it is in the field. Negative particles, likeelectrons, will go in the opposite direction as the arrows. In anelectric field, arrows will point away from positive particles and towards negative ones. So a proton in an electric field would move away from another proton, or towards an electron. Similar charges repel (push away from each other), while opposite charges attract (are pulled together).
Magnetic fields are a little different. They only push on moving charges, and they push more on charges that are moving faster. But they do not push at all on charges that are sitting still. However, a changing magnetic field can produce an electric field, and an electric field can push on any charges. This idea, calledelectromagnetic induction, is used to makeelectric generators, induction motors, andtransformers work. Together, electric and magnetic fields make up the electromagnetic field.
Before 1800, people thought that electricity and magnetism were two different things. However, this changed during the19th century when scientists likeHans Christian Ørsted andMichael Faraday proved that electricity and magnetism are actually connected. In 1820, Ørsted found that when he turned theelectric current from a battery on and off, it moved the needle on a nearby compass. When he studied this effect more carefully, he discovered that the electric current was producing a magnetic field. That is, when electric charges are moving, they can produce a force that pushes onmagnets. Ørsted had found one of the first connections between electricity and magnetism.
Faraday continued studying this connection, running tests with loops of wire and magnets. He found that if he set up two loops of wire and ran electricity through just one of them, he could (for a little while) produce an electric current in the other loop as well. Faraday also discovered that he could produce a current by moving a magnet through a loop of wire, or by moving the wire over a magnet. What Faraday had shown was that magnets could push back on moving electric charges, and that moving magnets could push on charges sitting still. This was like what Ørsted had found, but in reverse.
What's more, Maxwell's studies showed that light could be described as a ripple in the electromagnetic field. That is, light moves like awave. However, Maxwell's work did not agree withclassical mechanics, the description of forces and motion originally developed byNewton. Maxwell's equations predicted that light always moves through empty space atthe same speed. This was a problem because in classical mechanics, velocities are "additive"-- if a person A on a train moving at speed X throws a ball with speed Y, then a person B on the ground sees the ball moving with speed X+Y. According to Maxwell, if person A turns on a flashlight, they will see the light moving away from them at speedc. But person B on the ground must also see the light moving at speedc, notc+X. This led to the development of thetheory ofspecial relativity byEinstein, which explained how the speed of light could be the same for everyone, and why classical mechanics does not work for things moving very fast.
Electromagnetic radiation is thought to be both aparticle and awave. This is because it sometimes acts like a particle and sometimes acts like a wave. To make things easier we can think of an electromagnetic wave as a stream ofphotons (symbol γ).
Photons have energy andmomentum. When two charged objects push or pull on each other, they send photons back and forth. So photons carry the electromagnetic force between charged objects. Photons are also known asmessenger particles inphysics because these particles often carry messages between objects. Photons send messages saying "come closer" or "go away" depending on the charges of the objects that are being looked at. If a force exists while time passes, then photons are being exchanged during that time.
Fundamental electromagnetic interactions occur between any two particles that have an electric charge. These interactions involve the exchange or production of photons. Thus, photons are the carrier particles of electromagnetic interactions.
Electromagneticdecay processes can often be recognized by the fact that they produce one or more photons (also known asgamma rays). They proceed less rapidly than strong decay processes with comparable mass differences, but more rapidly than comparable weak decays.
