# Electromagnetic Waves

Electromagnetic waves are a form of energy transfer that occur when a changing magnetic field induces a changing electric field. These waves are made up of oscillating electric and magnetic fields, which are perpendicular to each other. Unlike mechanical waves, electromagnetic waves don't need a medium to travel through and can even go through a vacuum. Examples of electromagnetic waves include radio waves, microwaves, infrared waves, visible light, ultraviolet light, X-rays, and gamma rays.

Mechanical waves, on the other hand, are caused by vibrations in matter like solids, gases, and liquids. These waves travel through a medium by transferring energy from one particle to another. Examples of mechanical waves include sound waves and water waves.

## Discovery of electromagnetic waves

In 1801, Thomas Young conducted an experiment known as the double-slit experiment. During this experiment, he discovered that light behaves like a wave. He directed light through two small holes onto a flat surface and observed an interference pattern. Young also suggested that light was a transverse wave, rather than a longitudinal wave.

After Young's discovery, James Clerk Maxwell studied behaviour of electromagnetic waves. He summarized the relationship between magnetic and electrical waves in a set of equations called Maxwell's equations.

These equations helped scientists understand the fundamental nature of electromagnetic waves and how they interact with matter. Today, our understanding of electromagnetic waves is crucial in fields such as telecommunications, radio, and optics.

### Hertz’s experiment

In the late 1800s, Heinrich Hertz used Maxwell's equations to study radio waves. His experiments revealed that radio waves are actually a form of light.

Hertz conducted an experiment using two rods, a spark gap receiver connected to a circuit, and an antenna. When waves were detected, a spark was generated in the spark gap. These signals were found to have the same properties as electromagnetic waves. In fact, Hertz's experiment showed that radio waves and light waves travel at the same speed, but with different wavelengths and frequencies.

Thanks to Hertz's research, we now have a better understanding of the properties of radio waves and their similarities to other types of electromagnetic radiation. Today, we use radio waves for a variety of purposes, including communication, navigation, and scientific research.

The relationship between frequency, wavelength, and the speed of light is described by the equation:

c = f λ

where c is the speed of light, measured in meters per second (m/s), f is the frequency of the wave, measured in Hertz (Hz), and λ is the wavelength of the wave, measured in meters (m). In a vacuum, the speed of light is a constant value of approximately 3 x 10^8 m/s.

While electromagnetic waves were initially believed to exhibit only wave-like behavior, they can also display particle-like behavior. This concept is known as wave-particle duality. The shorter the wavelength, the more particle-like behavior the electromagnetic wave exhibits, and vice versa. As a result, electromagnetic radiation, including light, exhibits both wave-like and particle-like behavior. This dual nature of electromagnetic radiation is a fundamental concept in quantum mechanics and has profound implications for our understanding of the physical world.

## The properties of electromagnetic waves

Electromagnetic waves are unique in that they exhibit both wave-like and particle-like properties. The wave-like properties of electromagnetic waves include:

1. Electromagnetic waves are transverse waves, meaning that their oscillations are perpendicular to the direction of their propagation.
2. Electromagnetic waves can be reflected, refracted, diffracted, and produce interference patterns, similar to other types of waves.
3. Electromagnetic waves can exhibit polarization, which refers to the orientation of the electric and magnetic fields that make up the wave. The waves can have constant polarization or rotate with each cycle.

The particle-like properties of electromagnetic waves include:

1. Electromagnetic radiation consists of energized particles, such as photons, that create waves of energy with no mass.
2. Electromagnetic waves travel at the same speed in a vacuum, which is the same speed as the speed of light (3 x 10^8 m/s).
3. Electromagnetic waves can travel through a vacuum, meaning that they don't need a medium to transmit, unlike mechanical waves that require a medium to propagate.

The combination of these wave-like and particle-like properties is what makes electromagnetic waves so unique and important in our understanding of the physical world.

## What is the electromagnetic spectrum?

The electromagnetic spectrum is the entire spectrum of electromagnetic radiation made up of different types of electromagnetic waves. It is arranged according to frequency and wavelength: the left-hand side of the spectrum has the longest wavelength and lowest frequency, and the right-hand side has the shortest wavelength and highest frequency.

You can see the different types of electromagnetic waves that make up the entire electromagnetic radiation below.

## Types of electromagnetic waves

The electromagnetic radiation spectrum consists of a range of different types of waves with varying wavelengths and frequencies. The following are the different types of electromagnetic waves and their respective wavelengths and frequencies:

• Radio waves: 10^6 - 10^-4 m; 10^2 - 10^12 Hz- Microwaves: 10^-3 - 10^-4 m; 10^8 - 10^12 Hz
• Infrared: 10^-6 - 10^-3 m; 10^11 - 10^14 Hz
• Visible light: 4 x 10^-7 - 7 x 10^-7 m; 4 x 10^14 - 7.5 x 10^14 Hz
• Ultraviolet: 10^-8 - 10^-7 m; 10^15 - 10^17 Hz
• X-rays: 10^-11 - 10^-8 m; 10^17 - 10^20 Hz
• Gamma rays: <10^-10 m; >10^18 Hz

Each type of electromagnetic wave has different properties that make them useful for various applications. For example, radio waves are used for communication, while microwaves are used in microwave ovens and for satellite communication. Infrared radiation is used in remote controls and for heating, while visible light is used for illumination. Ultraviolet radiation is used in sterilization and for tanning, while X-rays are used in medical imaging. Gamma rays in cancer treatment and radiation therapy.

However, some types of electromagnetic waves can have harmful effects on living organisms. Microwaves, X-rays, and gamma rays, in particular, can be dangerous under certain circumstances, such as prolonged exposure or high-intensity radiation. It is important to understand the potential risks associated with exposure to electromagnetic radiation and take appropriate precautions to minimize these risks.

Radio waves are a type of electromagnetic radiation with the longest wavelength and the smallest frequency. They are able to travel long distances without significant attenuation, making them ideal for communication purposes. Radio waves are used in a variety of applications, including radio and television broadcasting, cellular communication, and satellite communication.

In the context of communication, radio waves are used to transmit coded information over long distances. This information can be in the form of audio, video, or data, and is typically transmitted in the form of electromagnetic waves using an antenna as a transmitter.

The process of transmitting and receiving radio waves involves encoding the information onto the wave, transmitting the wave through the air, and then decoding the information once the wave is received. This process is made possible by the unique properties of radio waves, which allow them to travel long distances without significant attenuation and be easily absorbed and detected by antennas.

Antennas are specialized devices that are designed to transmit and receive radio waves over a specific range of frequencies. They are typically composed of a conductive material, such as copper or aluminum, and come in a variety of shapes and sizes depending on their intended application.

Overall, radio waves are a critical component of modern communication systems, enabling us to transmit information across long distances quickly and efficiently.

## An example of an antenna, Unsplash

Microwaves are type of electromagnetic radiation with wavelengths ranging from 10 meters to centimeters. They have shorter wavelengths than radio waves, but longer wavelengths than infrared radiation. Microwaves are well transmitted through the atmosphere and have a variety of applications in modern technology.

One of the most well-known applications of microwaves is in the kitchen, where they are used heating food at high intensities. Microwaves generate heat by interacting with water molecules in the food, causing them to vibrate and generate heat through friction. This process is made possible by the high frequency of microwaves, which are easily absorbed by water molecules.

Microwaves are also widely used for communication purposes, such as in Wi-Fi and satellite communication. Due to their high frequency, microwaves can carry large amounts of information and transmit this information over long distances. This makes them ideal for communication applications, particularly those that require high bandwidths.

However, it is important to note that high-intensity microwaves can be harmful to living organisms, particularly internal organs that contain a high concentration of water molecules. Prolonged exposure to high-intensity microwaves can cause tissue damage and other health issues. Therefore, it is important to use caution when working with or near high-intensity microwaves and to take appropriate safety precautions to minimize the risk of exposure.

### Infrared

Infrared radiation, also known as infrared light, is a type of electromagnetic radiation with wavelengths ranging from millimeters to micrometers. Infrared radiation has a longer wavelength than visible light, which means that it is not visible to the human eye. However, it is still an important part of the electromagnetic spectrum and has many practical applications.

One of the most well-known applications of infrared radiation is in thermal imaging, which is used to detect heat signatures. All matter with a temperature greater than absolute zero emits thermal radiation in the form of infrared electromagnetic waves. This makes infrared radiation useful in a variety of applications, including thermal cameras and sensing devices.

Infrared radiation is also used in communication technologies, particularly in the form of infrared remote controls. Infrared signals can be transmitted through the atmosphere and are commonly used in home entertainment systems and other electronic devices.

In addition to these applications, infrared radiation is also used in medical imaging and diagnosis. Infrared thermal imaging can be used to detect changes in skin temperature, which can be indicative of a variety of medical conditions, including arthritis.

Overall, infrared radiation is an important part of the electromagnetic spectrum with a wide range of practical applications. From communication and sensing technologies to medical imaging and thermal imaging, infrared radiation plays an important role in many different fields.

### Visible light

Visible light is the part of the electromagnetic spectrum that can be seen by the human eye. Unlike other types of electromagnetic radiation, such as X-rays and ultraviolet radiation, visible light is not absorbed by the Earth's atmosphere. However, it can be scattered by gas and dust, which colors the sky, such as the blues and oranges seen during sunrise and sunset.

One of the most well-known applications of visible light is in photography, where light is used to capture images on film or digital sensors. Visible light is also in the display screens of televisions, smartphones, and other electronic devices.

Another important application of visible light is in fiber optic communication. Fiber optic cables use visible light to transmit data over long distances. The light is sent through the cables in pulses, which can carry a large amount of information quickly and efficiently.

In addition to these applications, visible light is also used in laser technology. Lasers emit a beam of light with waves of similar wavelengths, which allows the energy to be concentrated on a small spot. This makes lasers useful in a variety of applications, including surgery, manufacturing, and communication.

Overall, visible light is an important part of the electromagnetic spectrum with a wide range of practical applications. From photography and fiber optic communication to laser technology, visible light plays an essential role in many different fields.

### Ultraviolet light

Ultraviolet (UV) light is a type of electromagnetic radiation that lies between visible light and X-rays. When UV light illuminates any object that contains phosphorus, visible light is emitted that appears to glow. This phenomenon is used in various applications, such as curing or hardening some materials and detecting structural defects.

However, exposure to UV radiation can also pose health risks. Short-term exposure can cause sunburn, while long-term and high-intensity exposure can potentially harm living cells and cause premature aging of the skin and skin cancer.

Despite these risks, there are still many useful applications for UV light. One common use is in sun tanning, where exposure to UV radiation causes the skin to produce more melanin, which results in a darker skin tone. UV light is also used in fluorescent lighting, which is used for hardening materials and detecting structural defects in various industries. Additionally, UV light is used in sterilization processes to kill bacteria and other microorganisms.

Overall, UV light is an important part of the electromagnetic spectrum with both benefits and risks. From tanning and fluorescent lighting to sterilization, UV light plays a significant role in many different fields. However, it is essential to take precautions to limit exposure and ensure safety when working with UV radiation.

### X-rays

X-rays are highly energetic waves that can penetrate matter. They are a type of ionising radiation, meaning they have enough energy to displace electrons from the shells of atoms and convert them into ions. This type of ionising radiation can cause DNA mutations in living cells at high energies, which can lead to cancer.

X-rays emitted from objects in space are mostly absorbed by the Earth’s atmosphere, so they can only be observed using X-ray telescopes in orbit. X-rays are also used in medical and industrial imaging due to their penetrative characteristic.

X-ray absorption (or attenuation) allows us to use X-Rays to produce images. The dark and light areas on a radiograph image represent the intensity of X-Rays that reach the detector plate. They indicate the level of attenuation caused by the tissues between the source and detector.

X-ray absorption fine structure (XAFS) spectroscopy, also named X-ray absorption spectroscopy, is a technique that can be applied for a wide variety of disciplines because the measurements can be performed on solids, gasses, or liquids, including moist or dry soils, glasses, films, membranes, suspensions or pastes, and aqueous solutions.

X-ray interactions with matter include Rayleigh scattering, Compton scattering, photoelectric absorption, and pair production. Compton scattering and photoelectric absorption are the two most important interactions in diagnostic imaging. Pair production only occurs when photon energy is at least 1.02 MeV, which is not used by medical imaging.

### Gamma rays

Gamma rays are the highest energy waves and are created from the radioactive decay of an atomic nucleus. They have the shortest wavelength and the highest energy, which allows them to penetrate matter. Gamma rays are also a type of ionising radiation, which means they can damage living cells at high energies.

Gamma rays emitted from objects in space are mostly absorbed by the Earth’s atmosphere and can only be detected using gamma-ray telescopes in orbit.

Gamma rays have many applications due to their penetrating abilities. In medical treatments, gamma rays are used for radiotherapy to treat cancer and medical sterilisation to kill bacteria and viruses. In nuclear studies or nuclear reactors, gamma rays are used for imaging and to measure radiation levels. Gamma rays are also used in security applications, such as smoke detection and food sterilisation. In astronomy, gamma-ray telescopes are used to study the universe and detect gamma-ray bursts, which are some of the most energetic events in the universe.

Overall, gamma rays are a powerful and useful form of radiation with many applications in various fields. However, it is essential to take precautions and use them safely to avoid any potential harm they may cause.

A region of the sky centred on the pulsar Geminga. On the left is the total number of gamma rays detected by Fermi’s Large Area Telescope.

Electromagnetic waves consist of oscillating electric and magnetic fields that are perpendicular to each other. These waves can travel through a vacuum at the speed of light. Electromagnetic waves can also be reflected, refracted, polarised, and produce interference patterns, all of which demonstrate the wave-like behaviour of electromagnetic waves.

In addition to their wave-like characteristics, electromagnetic waves also possess particle properties. These particles are called photons, and their energy is dependent on the frequency of the electromagnetic waves they represent.

Electromagnetic waves are used for a variety of purposes. For example, radio waves are used for communication, microwaves are used for heating food, and X-rays and gamma rays are used for medical imaging and diagnostics. Electromagnetic waves are also used for sterilisation, such as in food and medical equipment.

In summary, electromagnetic waves are a fundamental aspect of our world and have many important applications in various fields. Understanding the properties and behaviours of electromagnetic waves is crucial for their safe and effective use.

## Electromagnetic Waves

What are electromagnetic waves?

Electromagnetic waves are oscillating transverse waves transferring energy.

What types of waves are electromagnetic waves?

Electromagnetic waves are transverse waves made from electromagnetic radiation that consists of synchronised oscillating electromagnetic fields created from the periodic movement of these fields.

What are examples of electromagnetic waves?

Examples of electromagnetic waves include radio waves, microwaves, infrared, visible light, ultraviolet, X-rays, and gamma rays.

What are the effects caused by electromagnetic waves?

Some effects caused by electromagnetic waves can be dangerous. For example, high-intensity microwaves can be harmful to living organisms and, more specifically, to internal organs. Ultraviolet radiation can cause sunburn. X-rays are a form of ionising radiation, which can cause DNA mutations in living cells at high energies. Gamma rays are also a form of ionising radiation

Are electromagnetic waves longitudinal or transverse?

All electromagnetic waves are transverse waves.