The way iron filings arrange themselves around a magnet clearly shows the north-south flow of a magnetic field.
In physics, the electromagnetic force is an influence that affects electrically charged particles. Along with gravity, it is the force that humans encounter most in everyday life and explains most of the phenomena that people are familiar with. It is responsible for electricity, magnetism and light; it holds electrons and protons together in atoms; and allows atoms to join together to form molecules and generate chemical reactions. This force is also responsible for the solidity of solid objects and is the reason why they cannot pass each other.
In an electric motor, applying electricity to a magnet causes it to rotate inside a metal casing.
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 only operates over an extremely short range. The electromagnetic force is the second strongest and, like gravity, operates over unlimited distances.
The Inverse Square Law
The 19th century physicist James Clerk Maxwell showed that light was a disturbance of the magnetic field.
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 power, the intensity is reduced to 1/25.
Positive and Negative Charges
Unlike gravity, the electromagnetic force is only felt by objects that have an electrical 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, for the most part, have no general electrical charge, they don’t feel the electromagnetic force, which explains why gravity, while a much weaker force, dominates on large scales.
A small electromagnet.
When two different materials rub together, electrons can move from one to the other, leaving one positively charged and the other negatively charged. The two will then attract and can be attracted to electrically neutral objects. This is known as static electricity and can be demonstrated by a number of simple experiments, such as rubbing a balloon with a piece of fur and sticking it to the wall – it is held there by electrostatic attraction.
Radio telescopes detect radio waves, a form of electromagnetic radiation, from space.
An electric current flows when electrons move along a wire or other conductor from a region with an excess of electrons to another 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 complete.
On the atomic scale, the attraction between positively charged protons in the nucleus and negatively charged electrons on the outside holds atoms together and allows them to bond together to form molecules and compounds. The protons in the nucleus are held in place by the strong nuclear force, which, on this extremely small scale, overcomes electromagnetic repulsion.
The concept of electromagnetic fields was 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 can deflect a compass needle and induce a current in another coil nearby. He also showed that a changing magnetic field can 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 around electrically charged or magnetic objects.
Later, in the 19th century, physicist James Clerk Maxwell produced a series of equations that not only explained the relationship between electricity and magnetism, but also showed that light was a wave-like disturbance of the electromagnetic field. He came to 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, where 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.
With Einstein’s investigation of the photoelectric effect, in which light can dislodge electrons from a metallic surface, came the discovery that electromagnetic radiation (EMR) can behave like particles as well as waves. These particles are called photons. Electrons in an atom can gain energy by absorbing a photon and lose energy by emitting it. 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 the exchange of particles, like photos in the case of the electromagnetic force. In order to explain this force in a manner that was consistent with quantum theory, the theory of quantum electrodynamics was developed. The idea is that the electromagnetic force is mediated by “virtual” photos that exist only fleetingly during interactions between charged particles. It explains all electromagnetic interactions and rigorous testing has proven that it is a very accurate theory.