What’s EM energy?

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Electromagnetic energy takes many forms, including light and heat, and travels at the speed of light. The entire range of wavelengths is known as the electromagnetic spectrum. Electromagnetic radiation can behave as waves or particles, known as photons. Quantum electrodynamics explains the particle behavior of EMR. EMR is produced when matter temporarily absorbs energy and releases it to descend to a lower energy state. The energy of the Sun is crucial for life on Earth, and most forms of technology rely heavily on electromagnetic energy. High-frequency EMR can damage cells and alter DNA, increasing the risk of cancer.

Electromagnetic energy is familiar to most people as light and heat, but it can take many other forms, such as radio waves and X-rays. These are all types of radiation originating from the electromagnetic force, which is responsible for all electrical phenomena and magnetic. Radiation travels at the speed of light similar to waves.
Unlike sound waves, electromagnetic waves do not require a medium to travel through and can travel through empty space. The wavelength can range from hundreds of yards (meters) down to subatomic scales. The entire range of wavelengths is known as the electromagnetic spectrum, of which visible light makes up only a small part. Despite the observed wave-like nature of electromagnetic radiation (EMR), it can also behave as if it is composed of tiny particles, known as photons.

Light, electricity and magnetism

The connection between light and electromagnetism was revealed in the 19th century by the work of physicist James Clerk Maxwell on electric and magnetic fields. Using the equations he developed, he found that the speed at which fields move through space was exactly the speed of light, and he concluded that light was a disturbance of these fields, traveling in the form of waves. His equations also showed that other forms of EMR with longer and shorter wavelengths were possible; these were later identified. Maxwell’s discoveries gave rise to the study of electrodynamics, according to which EMR consists of electric and magnetic fields oscillating at right angles to each other and to the direction of motion. This explained the wave nature of light, as observed in many experiments.

Wavelength, frequency and energy

Electromagnetic radiation can be described in terms of its wavelength – the distance between wave crests – or its frequency – the number of crests that pass by a fixed point during a given time interval. When moving in a vacuum, EMR always travels at the speed of light; therefore, the speed at which the crests travel does not vary, and the frequency depends only on the wavelength. A shorter wavelength indicates a higher frequency and higher energy. This means that high-energy gamma rays travel no faster than low-energy radio waves; instead, they have much shorter wavelengths and much higher frequencies.

The wave-particle duality

Electrodynamics was very successful in describing electromagnetic energy in terms of fields and waves, but in the early 20th century, Albert Einstein’s investigation of the photoelectric effect, in which light removes electrons from a metal surface , raised a problem. He discovered that the energy of the electrons depended entirely on the frequency, not the intensity, of the light. An increase in frequency produced higher energy electrons, but an increase in brightness made no difference. The results could be explained only if light consisted of discrete particles, later called photons, which transferred their energy to electrons. This has created a conundrum: observed at large scales, EMR behaves like waves, but its interactions with matter at the smallest scales can only be explained in terms of particles.

This is known as wave-particle duality. It emerged during the development of quantum theory and applies to everything on the subatomic scale; electrons, for example, can behave both as waves and as particles. There is no general consensus among scientists on what this duality about the nature of electromagnetic energy actually means.

Quantum electrodynamics
Eventually a new theory, known as quantum electrodynamics (QED), emerged to explain the particle behavior of EMR. According to QED, photons are the particles that carry the electromagnetic force, and the interactions of electrically charged objects are explained in terms of the production and absorption of these particles, which themselves carry no charge. QED is considered one of the most successful theories ever developed.
How electromagnetic energy is produced
Classical electrodynamics described the production of EMR in terms of the movement of electric charges, but a more modern explanation, in line with quantum theory, is based on the idea that the subatomic particles that make up matter can only occupy certain levels of fixed energy. Electromagnetic radiation is released by moving from a higher to a lower energy state. Left to its own devices, matter will always try to reach its lowest energy level.

EMR can be produced when matter temporarily absorbs energy, such as when heated, then releases it to descend to a lower level. A lower energy state can also be reached when atoms or molecules combine with each other in a chemical reaction. Combustion is a familiar example: Typically, a molecule combines with the oxygen in the air, forming products that collectively have less energy than the original molecule. This causes the release of electromagnetic energy in the form of a flame.
In the Sun’s core, four hydrogen nuclei combine, in a series of steps, to form a helium nucleus that has slightly less mass, and therefore less energy. This process is known as nuclear fusion. The excess energy is released in the form of high-frequency gamma rays which are absorbed by outer matter, which then emits this energy, mainly in the form of visible light and heat.

Electromagnetic energy, life and technology
The energy of the Sun is crucial for life on Earth. Sunlight warms the earth’s surface, which in turn warms the atmosphere, maintaining temperatures suitable for life and driving the planet’s weather systems. Plants use the sun’s electromagnetic energy for photosynthesis, the method by which they produce food. Solar energy is converted into chemical energy which powers the processes that allow plants to produce the glucose they need to survive from carbon dioxide and water. The byproduct of this reaction is oxygen, so photosynthesis is responsible for maintaining the planet’s oxygen levels.
Most forms of technology rely heavily on electromagnetic energy. The industrial revolution was fueled by the heat generated by the burning of fossil fuels, and more recently, solar radiation has been used directly to provide “clean” and renewable energy. Modern communications, broadcasting and the internet are heavily dependent on radio waves and light channeled through fiber optic cables. Laser technology uses light to read and write to CDs and DVDs. Most of what scientists know about the universe comes from EMR analysis of various wavelengths of distant stars and galaxies.
Health effects
High-frequency EMR, such as gamma rays, X-rays and ultraviolet light, carry enough energy to cause chemical changes in biological molecules. It can break chemical bonds or remove electrons from atoms, forming ions. This can damage cells and alter DNA, increasing the risk of cancer. Concerns have also been raised about the health effects of low-frequency EMR, such as the radio waves and microwaves used by cell phones and other communication devices. While these forms of radiation appear to have no direct effect on the chemistry of life, they can cause tissue heating in localized areas with prolonged exposure. So far there seems to be no conclusive evidence that this can make people sick.

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