The electromagnetic force is one of the four fundamental forces of nature, responsible for electricity, magnetism, and light. It operates over unlimited distances and follows the inverse square law. Objects with different charges attract each other, while those with the same type repel each other. The force is mediated by “virtual” photons, and the theory of quantum electrodynamics explains all electromagnetic interactions.
In physics, the electromagnetic force is an influence affecting electrically charged particles. Along with gravity, it is the force humans encounter most every day and explains most of the phenomena people are familiar with. It is responsible for electricity, magnetism and light; holds electrons and protons together in atoms; and allows atoms to bond together to form molecules and drive chemical reactions. This force is also responsible for the solidity of solid objects and is the reason they cannot pass through each other.
The electromagnetic force is one of the four fundamental forces of nature. The other three are the gravitational force, the strong nuclear force and the weak nuclear force. The strong nuclear force is the strongest of these, but it operates only over an extremely short range. The electromagnetic force is the second strongest and, like gravity, operates over unlimited distances.
The inverse square law
Like gravity, the electromagnetic force follows the inverse square law. This means that the strength of the force is inversely proportional to the square of the distance from its source. So, for example, if someone moves 5 units away from the source of the force, the intensity is reduced to 1/25th.
Positive and negative charges
Unlike gravity, the electromagnetic force is only felt by objects that have an electric charge, which can be positive or negative. Objects with different types of charges attract each other, but those with the same type repel each other. This means that the force can be attractive or repulsive, depending on the charges involved. Since most objects, more often than not, have no overall electric charge, they don’t feel the electromagnetic force, which explains why gravity, although a much weaker force, dominates on large scales.
When two different materials rub together, electrons can move from one to the other, leaving one with a positive charge and the other with a negative charge. The two then attract each other and can be attracted to electrically neutral objects. This is known as static electricity and can be demonstrated by various simple experiments, such as rubbing a balloon with a piece of fur and sticking it to a wall – it is held there by electrostatic attraction.
An electric current flows when electrons move along a wire or other conductor from a region with an excess of electrons to one where there is a deficit. Current is said to flow from negative to positive. In a simple circuit using a battery, electrons flow from the positive to the negative terminal when the circuit is completed.
On the atomic scale, the attraction between the positively charged protons in the nucleus and the negatively charged electrons outside holds atoms together and allows them to bond with each other to form molecules and compounds. The protons in the nucleus are held in place by the strong nuclear force, which, at this extremely small scale, overcomes electromagnetic repulsion.
Electromagnetic fields
The concept of electromagnetic fields was first developed by scientist Michael Faraday in the early 19th century. He showed that electrically charged and magnetized objects can influence each other from a distance. For example, an electric current flowing through a coil of wire could deflect a compass needle and induce a current in another nearby coil. He also showed that a changing magnetic field could produce an electric current in a wire. This established a connection between electricity and magnetism and the existence of a field that varies with distance surrounding electrically charged or magnetic objects.
Later in the 19th century, physicist James Clerk Maxwell produced a set of equations that explained not only the relationship between electricity and magnetism, but also showed that light was a wave-like disturbance of the electromagnetic field. He reached this conclusion when he calculated the speed at which electromagnetic influences travel and found that this was always the speed of light. The implication was that light was a form of electromagnetic radiation that traveled as waves. This led to the theory of classical electrodynamics, in which an electromagnetic wave is generated by a moving electric charge. The movement of a coil of wire in a magnetic field can generate low-energy radio waves, while the more energetic movement of electrons in a hot wire can generate visible light.
Quantum electrodynamics
With Einstein’s investigation of the photoelectric effect, in which light can strip electrons from a metal surface, came the discovery that electromagnetic radiation (EMR) can behave like particles as well as waves. These particles are called photons. The electrons in an atom can gain energy by absorbing a photon and lose energy by emitting one. In this way, EMR can be explained as the emission of photons when electrons experience a drop in energy levels.
According to quantum theory, all four forces of nature can be explained in terms of particle exchange, such as photos in the case of the electromagnetic force. To explain this force in a way that is consistent with quantum theory, the theory of quantum electrodynamics was developed. The idea is that the electromagnetic force is mediated by “virtual” photons that exist only fleetingly during interactions between charged particles. It explains all electromagnetic interactions and rigorous testing has shown it to be a very accurate theory.
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