Electricity can exist in a static form, as seen in situations where it causes hair to stand on end. Similarly, magnetism can also be static. When a magnetic field undergoes changes, it can induce corresponding changes in an electric field and vice versa, thereby establishing a connection between the two. These changes in the fields give rise to electromagnetic waves, which differ from mechanical waves in that they do not necessitate a medium for their propagation. Hence, electromagnetic waves can travel through not only air and solid materials but also through the vacuum of space.
Electromagnetic waves travel at the speed of light in a vacuum, and it is represented by the symbol c. When these waves pass through homogeneous and isotropic media, the electric and magnetic fields oscillate perpendicular to each other. The direction of energy and wave propagation also behaves identically. This perpendicular oscillation gives rise to a transverse wave. The location of an electromagnetic wave in the electromagnetic spectrum can be identified either by its frequency of oscillation or its wavelength.
Electromagnetic waves with varying frequencies are given different names as they are generated from different phenomena and have distinct effects on matter. The different types of electromagnetic waves are arranged in the order of increasing frequency and decreasing wavelength. They are radio, microwave radiation, infrared radiation, visible light (including ultraviolet), ultraviolet radiation, X-rays, and gamma radiation, respectively.
Now, let’s analyse the important uses of electromagnetic radiation.
Uses of Electromagnetic Radiation
Similar to all other electromagnetic waves, radio waves travel at the speed of light in a vacuum and at a slightly lower speed in the Earth’s atmosphere. Radio waves are produced by charged particles that undergo acceleration, such as electric currents that vary with time. Radio waves that occur naturally are emitted by astronomical objects and lightning, and they form a component of the blackbody radiation emitted by all warm objects.
Radio waves have wavelengths that span from a few millimetres to hundreds of kilometres. The communication industry uses the lowest-frequency waves, including radio waves, to transmit signals. Television broadcasting, AM and FM radio broadcasts, military communications, ham radio, mobile phones, wireless computer networks, and other communication media employ various frequencies of radio waves.
Microwave radiation falls within the electromagnetic spectrum, with wavelengths ranging from about one metre to one millimetre and corresponding frequencies between 300 MHz and 300 GHz, respectively. The frequency of microwaves is second to last on the electromagnetic spectrum. Due to their high frequency, microwaves have the ability to penetrate obstacles and objects.
Narrow beams of microwaves can be conveniently produced using small, high-gain antennas with a diameter ranging from half a metre to 5 metres due to their short wavelength. This feature makes microwaves suitable for point-to-point communication links and radar applications. Wireless devices like cell phones, cordless phones, laptops with wireless LAN (Wi-Fi) access, and Bluetooth earphones commonly utilise microwave frequencies. The types of antennas used include rubber ducky antennas, short whip antennas, patch antennas, sleeve dipoles, and the printed circuit inverted F antenna (PIFA), which is increasingly used in cell phones.
Infrared radiation, also referred to as infrared light, is a form of electromagnetic radiation that has wavelengths longer than those of visible light, making it invisible to the human eye. However, humans can perceive certain IR wavelengths, up to 1050 nanometres, emitted from pulsed lasers under specific conditions. Infrared light encompasses a range of wavelengths between 700 nanometres, which is at the red edge of the visible spectrum, and 1 millimetre. The majority of thermal radiation emitted by objects near room temperature is in the form of infrared radiation.
Infrared radiation with higher wavelengths has a greater capacity for producing heat, while infrared radiation with lower wavelengths generates less heat and is applied in imaging technologies and remote controls. Infrared radiation is employed in night vision equipment when there is insufficient visible light for observation. It can also be used to determine the temperature of objects remotely, provided that the emissivity of the object is known. In infrared photography, the near-infrared spectrum is captured using infrared filters. Digital cameras typically incorporate infrared blockers. However, cheaper digital cameras and camera phones utilise less effective filters and can detect intense near-infrared radiation, appearing as a bright purple-white colour.
Visible Light Rays
Visible light is the portion of the electromagnetic spectrum that is perceptible to humans. Visible light is produced by anything that glows or emits light. While the sun, light bulbs, candles, and fire are commonly associated with light, visible light emanates from numerous sources and appears in various colours.
Visible light has three primary applications: fibre optic communication, photography, and electronic devices. Visible light is also used in television and computer screens, glow sticks, and fireworks. It falls within the electromagnetic spectrum between infrared and ultraviolet radiation.
Ultraviolet (UV) radiation is a type of electromagnetic radiation with a shorter wavelength than visible light but a longer wavelength than X-rays. Approximately 10% of the total electromagnetic radiation emanating from the sun is composed of UV radiation. While UV radiation is invisible to the human eye, certain insects, including bumblebees, are capable of detecting it.
UV radiation has wide applications in industrial processes and medical and dental practices for various purposes, such as sterilisation, creating fluorescent effects, curing inks and resins, phototherapy, and tanning. Natural sources of UV radiation include sunlight, and its applications can be found in various fields. UV light has various applications in both commercial and industrial settings, including air purification, water treatment, skin treatment, indoor gardening, and item identification, among others, using UV lamps. Additionally, UV light is used to analyse the chemical structure of compounds by inducing a colour change. A device called a spectrophotometer is used to do this task, which involves transmitting a beam of UV light through the solution.
X-rays, also known as X-radiation, are a type of electromagnetic radiation with high energy that can penetrate through materials. Compared to UV rays, X-rays have shorter wavelengths, while their wavelengths are usually longer than gamma rays. Röntgen radiation is another term used in various fields to describe X-radiation, which belongs to the high-energy wave category.
X-rays serve multiple purposes, such as identifying fractures in human bones in medical settings, scanning luggage of passengers in airports and other transportation hubs, studying the structures and environments of celestial objects, detecting defects in welds, and even restoring ancient paintings.
Of all the waves in the electromagnetic spectrum, gamma rays have the highest energy and the shortest wavelengths. They originate from the most energetic and hottest celestial objects, such as pulsars, neutron stars, supernova explosions, and areas surrounding black holes. On our planet, gamma waves are produced by nuclear detonations, lightning, and the comparatively less dramatic process of radioactive decay.
Gamma rays are utilised in various fields, including medicine, due to their high frequency and shorter wavelengths. They have the capability to detect imperfections like cracks, faults, and holes in metals. Additionally, they play a role in the production of diverse products, ranging from food to silicon chips, plastics, and paints. As a form of high-energy, short-wavelength electromagnetic radiation, gamma rays are capable of eliminating cells that need to be eradicated, such as cancer cells. Hence, gamma rays are used in medical applications to treat various diseases, including cancer.