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Rainbows are an optical phenomenon that occur due to the refraction and reflection of light. Rainbows occur when water droplets in the atmosphere refract, reflect, and disperse sunlight into its spectral colors. These colors are diverted to the eye of the observer, allowing this phenomenon to be seen.

The colors of the rainbow we see are made up of electromagnetic radiation, or a form of energy. The types of electromagnetic radiation are gamma rays, x-rays, ultraviolet rays, visible light, infrared rays, radio waves, and microwaves. Visible light is between infrared and ultraviolet rays which is where a rainbow can be seen.

The colors from the rainbow, known as Roy G Biv, are made up of several different wavelengths. Each wavelength has their own properties and can be seen in the rainbow with how long and short each color is. The color red has the longest wavelength, so it can be seen at the top of the rainbow. The colors indigo and violet have the shortest so it is seen at the bottom. Sometimes the eye can have difficulty setting the 2 colors apart and will sometimes combine them to form purple.

Any time it rains, we expect to see a rainbow, but there are certain conditions that must be met in order for this phenomenon to occur. Most importantly, the sun must be out. Without the sun, the refraction and reflection of sunlight cannot occur. In order to see a rainbow, one needs to be standing with the sun on their back and the rain droplets in front of them. Rainbows also require the sun to be less than 42 degrees above the horizon so the rays from the sun can hit the raindrops to create a rainbow.

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screenshot of contact proof (shreveport weather)

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Matt Hemmingway, Senior Meteorologist- National Weather Service (Shreveport, LA)

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Evidence of Communication with Expert (Response)

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Evidence of Communication with Expert (Response)

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Happy Pride, Short Wave Listeners! Here's a fun episode from our archives to celebrate the month!

It's another "Back To School" episode where we take a concept you were maybe taught in school as a kid, but didn't really learn or just forgot.

Short Wave producer Thomas Lu and host Maddie Sofia go on a journey to explore what a rainbow exactly is and how we see them...with some help from Kerstin Nordstrom, professor of physics at Mount Holyoke College.

Email us your Back-To-School ideas at shortwave@npr.org.
This episode was produced and reported by Thomas Lu, edited by Viet Le and fact-checked by Ariela Zebede. The audio engineer for this episode was J Czys.

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Rainbows! How They Form And Why We See Them : Short Wave

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Happy Pride, Short Wave Listeners! Here's a fun episode from our archives to celebrate the month!It's another "Back To School" episode where we take a concept you were maybe taught in school as a kid, but didn't really learn or just forgot.

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"A rainbow in the east will be followed by a fine morrow, in the west by a wet day." - Weather Proverb

What is a rainbow?

The rainbow is one of the more spectacular light shows observed on earth. The traditional rainbow is sunlight spread out into its spectru m of colors and diverted to the eye of the observer by water droplets. The "bow" part of the word refers to the fact that the rainbow is a group of nearly circular arcs of color all having a common center. Typically, we only see a portion of the entire circle, leading to the bow shape.

What makes the bow?

To understand how the bow is formed, we need to consider the path of a ray of sunlight through a single round raindrop. As light enters the raindrop, it is refracted (the path of the light is bent to a different angle), and some of the light is reflected by the internal, curved, mirror-like surface of the raindrop, and finally is refracted back out the raindrop toward the observer.

This schematic represents the path of one light ray entering a raindrop at point A. As the light beam enters the surface of the rain drop, it is bent (refracted) a little and instead of continuing to point D, strikes the inside wall of the raindrop at point B, where it is reflected back to point C. As it emerges from the raindrop, it is ref racted (bent) again into the direction E. The angle created at point D is 42 degrees.

The ray drawn here is significant because it represents the ray that has the smallest angle of deviation of all the rays that can enter the raindrop. This means that much of the sunlight that is refracted and reflected through the raindrop is focused along this path. This is known as the rainbow ray. Since the various colors that make up white light all have slightly different wavelengths, each color becomes slightly separated from the others as the light ray is refracted and reflected. So, rays that strike the raindrop at this angle of 42 o will tend to form a concentrated, strong beam in which the colors will be widely separated. This creates the color bands in the rainbow, with blue along the inner portion of the bow, and red on the outside edge of the bow.

Since the raindrop is circular, the reflection it creates is also circular. We don't see a full circular rainbow however, because the earth gets in the way. The lower the sun is to the horizon, the more of the circle we see. At sunset, we would see a full semi-circle of the rainbow with the top of the arch 42 o above the horizon. The higher the sun is in the sky, the smaller the arch of the rainbow above the horizon. If the sun is more than 42 o above the horizon, no rainbow will be visible.

So, the main ingredients to see a rainbow are the following:

You need to be standing with the sun to your back and the rain in front of you.

The sun needs to be less than 42o above the horizon.

The sun's rays must be hitting the raindrops to create the rainbow.

What makes a double rainbow?

Sometimes we see two rainbows at once. What causes this? We have followed the path of a ray of light as it enters and is reflected inside the raindrop. But, not all of the energy of the ray escapes the raindrop after it is reflected once. A part of the ray is reflected again, and travels along a different path inside the drop to emerge from the drop at a different angle. The rainbow we normally see is called the primary rainbow and is produced from one internal reflection. The secondary rainbow arises from two internal reflections and the rays exit the drop the second time at an angle of around 50 o, rather than the 42 o for the primary rainbow. This effect produces the secondary rainbow, with the colors reversed from the primary rainbow. It is possible for light to be reflected more than twice within a raindrop, but these additional rainbows are typically never seen under normal circumstances.

Why did people in Ireland believe there was gold at the end of rainbows?

Even as far back as the 17th century, people knew that we cannot see the complete circle of the rainbow, and instead we see only a portion of it, in the shape of a bow. In Ireland, people in the 17th century became fond of saying that one was as likely to find a pot of gold as to find the end of the rainbow. The expression somehow changed, and became a part of mythology.

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"A rainbow in the east will be followed by a fine morrow, in the west by a wet day." - Weather Proverb The rainbow is one of the more spectacular light shows observed on earth. The traditional rainbow is sunlight spread out into its spectrum of colors and diverted to the eye of the observer by water droplets.

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A rainbow is a multicolored arc made by light striking water droplets. The most familiar type rainbow is produced when sunlight strikes raindrops in front of a viewer at a precise angle (42 degrees). Rainbows can also be viewed around fog, sea spray, or waterfalls. A rainbow is an optical illusion-it does not actually exist in a specific spot in the sky. The appearance of a rainbow depends on where you're standing and where the sun (or other source of light) is shining. The sun or other source of light is usually behind the person seeing the rainbow. In fact, the center of a primary rainbow is the antisolar point, the imaginary point exactly opposite the sun. Rainbows are the result of the refraction and reflection of light. Both refraction and reflection are phenomena that involve a change in a wave's direction. A refracted wave may appear "bent", while a reflected wave might seem to "bounce back" from a surface or other wavefront. Light entering a water droplet is refracted. It is then reflected by the back of the droplet. As this reflected light leaves the droplet, it is refracted again, at multiple angles. The radius of a rainbow is determined by the water droplets' refractive index. A refractive index is the measure of how much a ray of light refracts (bends) as it passes from one medium to another-from air to water, for example. A droplet with a high refractive index will help produce a rainbow with a smaller radius. Saltwater has a higher refractive index than freshwater, for instance, so rainbows formed by sea spray will be smaller than rainbows formed by rain. Rainbows are actually full circles. The antisolar point is the center of the circle. Viewers in aircraft can sometimes see these circular rainbows. Viewers on the ground can only see the light reflected by raindrops above the horizon. Because each person's horizon is a little different, no one actually sees a full rainbow from the ground. In fact, no one sees the same rainbow-each person has a different antisolar point, each person has a different horizon. Someone who appears below or near the "end" of a rainbow to one viewer will see another rainbow, extending from his or her own horizon. Colors A rainbow shows up as a spectrum of light: a band of familiar colors that include red, orange, yellow, green, blue, and violet. The name "Roy G. Biv" is an easy way to remember the colors of the rainbow, and the order in which they appear: red, orange, yellow, green, blue, indigo, and violet. (Many scientists, however, think "indigo" is too close to blue to be truly distinguishable.) White light is how our eyes perceive all the colors of the rainbow mixed together. Sunlight appears white. When sunlight hits a rain droplet, some of the light is reflected. The electromagnetic spectrum is made of light with many different wavelengths, and each is reflected at a different angle. Thus, spectrum is separated, producing a rainbow. Red has the longest wavelength of visible light, about 650 nanometers. It usually appears on the outer part of a rainbow's arch. Violet has the shortest wavelength (about 400 nanometers) and it usually appears on the inner arch of the rainbow. At their edges, the colors of a rainbow actually overlap. This produces a sheen of "white" light, making the inside of a rainbow much brighter than the outside. Visible light is only part of a rainbow. Infrared radiation exists just beyond visible red light, while ultraviolet is just beyond violet. There are also radio waves (beyond infrared), x-rays (beyond ultraviolet), and gamma radiation (beyond x-rays). Scientists use an instrument called a spectrometer to study these invisible parts of the rainbow. Rainbow Variations GlowThe atmosphere opposite a rainbow, facing the sun, is often glowing. This glow appears when rain or drizzle is falling between the viewer and the sun. The glow is formed by light passing through raindrops, not reflected by them. Some scientists call this glow a zero-order glow. Double RainbowSometimes, a viewer may see a "double rainbow." In this phenomenon, a faint, secondary rainbow appears above the primary one. Double rainbows are caused by light being reflected twice inside the raindrop. As a result of this second reflection, the spectrum of the secondary rainbow is reversed: red is on the inner section of the arch, while violet is on the outside. Higher-Order RainbowsLight can be reflected from many angles inside the raindrop. A rainbow's "order" is its reflective number. (Primary rainbows are first-order rainbows, while secondary rainbows are second-order rainbows.) Higher-order rainbows appear to viewers facing both toward and away from the sun. A tertiary rainbow, for example, appears to a viewer facing the sun. Tertiary rainbows are third-order rainbows-the third reflection of light. Their spectrum is the same as the primary rainbow. Tertiary rainbows are difficult to see for three main reasons. First, the viewer is looking toward the sun-the center of a tertiary rainbow is not the antisolar point, it's the sun itself. Second, tertiary rainbows are much, much fainter than primary or secondary rainbows. Finally, tertiary rainbows are much, much broader than primary and secondary rainbows. Quaternary rainbows are fourth-order rainbows, and also appear to viewers facing the sun. They are even fainter and broader than tertiary rainbows. Beyond quaternary rainbows, higher-order rainbows are named by their reflective number, or order. In the lab, scientists have detected a 200th-order rainbow. Twinned RainbowA twinned rainbow is two distinct rainbows produced from a single endpoint. Twinned rainbows are the result of light hitting an air mass with different sizes and shapes of water droplets-usually a raincloud with different sizes and shapes of raindrops. destructive interference. Light is either reinforced (constructive interference) or canceled out (destructive interference). Interference is responsible for the lighter hues and narrower bands of supernumeraries. Reflection RainbowA reflection rainbow appears above a body of water. A primary rainbow is reflected by the water, and the reflected light produces a reflection rainbow. Reflection rainbows do not mirror the primary rainbow-they often appear to stretch above it. Reflected RainbowA reflected rainbow appears directly on the surface of a body of water. A reflected rainbow is created by rays of light reflected by the water surface, after the rays have have passed through water droplets. Reflected rainbows to not appear to form a circle with a primary rainbow, although their endpoints seem to meet in an almond-shaped formation. Red RainbowA red rainbow, also called a monochrome rainbow, usually appears at sunrise or sunset. During this time, sunlight travels further in the atmosphere, and shorter wavelengths (blue and violet) have been scattered. Only the long-wavelength red colors are visible in this rainbow. FogbowA fogbow is formed in much the same way as a primary rainbow. Light in a fogbow is refracted and reflected by fog (water droplets suspended in air). A fogbow seen in the clouds is called a cloudbow. Because the water droplets in fog are much smaller than raindrops, fogbows have much fainter colors than rainbows. In fact, some fogbows have few detectable colors at all and appear mostly white, with a reddish tinge on their outer edge and a bluish tinge on their inner edge. MoonbowA moonbow, also called a lunar rainbow, is a rainbow produced by light reflected by the Moon. The Moon itself does not emit light, of course. Moonlight is reflected sunlight, as well as some starlight and "Earthlight." Because moonlight is so much fainter than sunlight, moonbows are dimmer than rainbows. Rainbows in Myth Rainbows are part of the myths of many cultures around the world. Rainbows are often portrayed as bridges between people and supernatural beings. In Norse mythology, for instance, a rainbow called the Bifrost connects Earth with Asgard, where the gods live. In the ancient beliefs of Japan and Gabon, rainbows were the bridges that human ancestors took to descend to the planet. The shape of a rainbow also resembles the bow of an archer. Hindu culture teaches that the god Indra uses his rainbow bow to shoot arrows of lightning. Rainbows are usually positive symbols in myths and legends. In the Epic of Gilgamesh and, later, the Bible, the rainbow is a symbol from a deity (the goddess Ishtar and the Hebrew God) to never again destroy the Earth with floods. Sometimes, however, rainbows are negative symbols. In parts of Burma, for instance, rainbows are considered demons that threaten children. Tribes throughout the Amazon basin associate rainbows with disease. Perhaps the most famous piece of mythology surrounding rainbows is the Irish legend of the pot of gold at the end of a rainbow. The gold is guarded by a tricky leprechaun, but-because no one sees the same rainbow and rainbows don't "end" (they're circles)-no one ever finds the gold or the magical creature. Rainbow Flags Rainbow flags usually appear as stripes (bands) of at least five different colors. Rainbow flags have long represented groups championing diversity, respect, and inclusiveness. The Wiphala is a type of rainbow flag. It is a symbol of communities indigenous to the Andes Mountains, stretching from modern-day Ecuador to Chile. A Wiphala has been an official flag of Bolivia since 2009, when the nation elected its first indigenous president, Evo Morales. The Wiphala features a diagonal patchwork design with squares in different rainbow colors. Different arrangements of patchwork squares represent different Andean communities. The Buddhist flag, designed in the 19th century, is flown by Buddhists around the world. It is a vertical arrangement of six bands, each representing a different aspect of Buddhism, from kindness to moderation, blessings to wisdom. The Jewish Autonomous Oblast, a community on Russia's border with China, is represented by a seven-banded rainbow flag. The seven bands symbolize the seven branches of a menorah. The most familiar rainbow flag may be the banner representing the movement supporting civil rights for members of the lesbian, gay, bisexual, and transgender (LGBT) community. The different colors of the "LGBT pride" flag represent the diverse community itself, as well as different aspects associated with each color. Orange, for example, symbolizes health and healing, while green symbolizes nature. Supernumerary Rainbow A supernumerary rainbow is a thin, pastel-colored arc usually appearing below the inner arch of a rainbow. Supernumeraries are the result of the complex interaction of light rays in an air mass with small, similarly sized water droplets. In supernumerary formation, reflected rays interact in ways called constructive and

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A rainbow is a multicolored arc made by light striking water droplets. The most familiar type rainbow is produced when sunlight strikes raindrops in front of a viewer at a precise angle (42 degrees). Rainbows can also be viewed around fog, sea spray, or waterfalls.

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By the end of this section, you will be able to:

Explain the phenomenon of dispersion and discuss its advantages and disadvantages.

Everyone enjoys the spectacle of a rainbow glimmering against a dark stormy sky. How does sunlight falling on clear drops of rain get broken into the rainbow of colors we see? The same process causes white light to be broken into colors by a clear glass prism or a diamond. (See Figure 1.)

Figure \(\PageIndex{1}\): The colors of the rainbow (a) and those produced by a prism (b) are identical. (credit: Alfredo55, Wikimedia Commons; NASA)

We see about six colors in a rainbow -- red, orange, yellow, green, blue, and violet; sometimes indigo is listed, too. Those colors are associated with different wavelengths of light, as shown in Figure 1. When our eye receives pure-wavelength light, we tend to see only one of the six colors, depending on wavelength. The thousands of other hues we can sense in other situations are our eye's response to various mixtures of wavelengths. White light, in particular, is a fairly uniform mixture of all visible wavelengths. Sunlight, considered to be white, actually appears to be a bit yellow because of its mixture of wavelengths, but it does contain all visible wavelengths. The sequence of colors in rainbows is the same sequence as the colors plotted versus wavelength in Figure 2. What this implies is that white light is spread out according to wavelength in a rainbow. Dispersion is defined as the spreading of white light into its full spectrum of wavelengths. More technically, dispersion occurs whenever there is a process that changes the direction of light in a manner that depends on wavelength. Dispersion, as a general phenomenon, can occur for any type of wave and always involves wavelength-dependent processes.

DISPERSION

Dispersion is defined to be the spreading of white light into its full spectrum of wavelengths.

Figure \(\PageIndex{2}\): Even though rainbows are associated with seven colors, the rainbow is a continuous distribution of colors according to wavelengths.

Refraction is responsible for dispersion in rainbows and many other situations. The angle of refraction depends on the index of refraction, as we saw in "The Law of Refraction." We know that the index of refraction \(n\) depends on the medium. But for a given medium, \(n\) also depends on wavelength (Table \(\PageIndex{1}\)). Note that, for a given medium, \(n\) increases as wavelength decreases and is greatest for violet light. Thus violet light is bent more than red light, as shown for a prism in Figure 3 and the light is dispersed into the same sequence of wavelengths as seen in 1 and 2.

MAKING CONNECTIONS: DISPERSION

Any type of wave can exhibit dispersion. Sound waves, all types of electromagnetic waves, and water waves can be dispersed according to wavelength. Dispersion occurs whenever the speed of propagation depends on wavelength, thus separating and spreading out various wavelengths. Dispersion may require special circumstances and can result in spectacular displays such as in the production of a rainbow. This is also true for sound, since all frequencies ordinarily travel at the same speed. If you listen to sound through a long tube, such as a vacuum cleaner hose, you can easily hear it is dispersed by interaction with the tube. Dispersion, in fact, can reveal a great deal about what the wave has encountered that disperses its wavelengths. The dispersion of electromagnetic radiation from outer space, for example, has revealed much about what exists between the stars -- the so-called empty space.

Medium

Red (660 nm)

Orange (610 nm)

Yellow (580 nm)

Green (550 nm)

Blue (470 nm)

Violet (410 nm)

Figure \(\PageIndex{3}\): (a) A pure wavelength of light falls onto a prism and is refracted at both surfaces. (b) White light is dispersed by the prism (shown exaggerated). Since the index of refraction varies with wavelength, the angles of refraction vary with wavelength. A sequence of red to violet is produced, because the index of refraction increases steadily with decreasing wavelength.

Rainbows are produced by a combination of refraction and reflection. You may have noticed that you see a rainbow only when you look away from the sun. Light enters a drop of water and is reflected from the back of the drop, as shown in Figure 4. The light is refracted both as it enters and as it leaves the drop. Since the index of refraction of water varies with wavelength, the light is dispersed, and a rainbow is observed, as shown in Figure 5a. (There is no dispersion caused by reflection at the back surface, since the law of reflection does not depend on wavelength.) The actual rainbow of colors seen by an observer depends on the myriad of rays being refracted and reflected toward the observer's eyes from numerous drops of water. The effect is most spectacular when the background is dark, as in stormy weather, but can also be observed in waterfalls and lawn sprinklers. The arc of a rainbow comes from the need to be looking at a specific angle relative to the direction of the sun, as illustrated in Figure 5b. (If there are two reflections of light within the water drop, another "secondary" rainbow is produced. This rare event produces an arc that lies above the primary rainbow arc -- see Figure 5c.)

RAINBOWS

Rainbows are produced by a combination of refraction and reflection.

Figure \(\PageIndex{4}\): Part of the light falling on this water drop enters and is reflected from the back of the drop. This light is refracted and dispersed both as it enters and as it leaves the drop.

Figure \(\PageIndex{5}\): (a) Different colors emerge in different directions, and so you must look at different locations to see the various colors of a rainbow. (b) The arc of a rainbow results from the fact that a line between the observer and any point on the arc must make the correct angle with the parallel rays of sunlight to receive the refracted rays. (c) Double rainbow. (credit: Nicholas, Wikimedia Commons)

Dispersion may produce beautiful rainbows, but it can cause problems in optical systems. White light used to transmit messages in a fiber is dispersed, spreading out in time and eventually overlapping with other messages. Since a laser produces a nearly pure wavelength, its light experiences little dispersion, an advantage over white light for transmission of information. In contrast, dispersion of electromagnetic waves coming to us from outer space can be used to determine the amount of matter they pass through. As with many phenomena, dispersion can be useful or a nuisance, depending on the situation and our human goals.

PHET EXPLORATIONS: GEOMETRIC OPTICS

How does a lens form an image? See how light rays are refracted by a lens. Watch how the image changes when you adjust the focal length of the lens, move the object, move the lens, or move the screen.

Summary

The spreading of white light into its full spectrum of wavelengths is called dispersion.

Rainbows are produced by a combination of refraction and reflection and involve the dispersion of sunlight into a continuous distribution of colors.

Dispersion produces beautiful rainbows but also causes problems in certain optical systems.

Glossary

dispersion

spreading of white light into its full spectrum of wavelengths

rainbow

dispersion of sunlight into a continuous distribution of colors according to wavelength, produced by the refraction and reflection of sunlight by water droplets in the sky

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The spreading of white light into its full spectrum of wavelengths is called dispersion. Rainbows are produced by a combination of refraction and reflection and involve the dispersion of sunlight ...

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Electromagnetic radiation, or EM radiation, is a fundamental form of energy that surrounds us everywhere, from the microwaves that heat our food to the radio waves that bring us music and news. In this article, we will explore electromagnetic radiation, its nature, theory, properties, and the wide range of forms it takes.

What is Electromagnetic Radiation?

Electromagnetic radiation can be defined as a form of energy that is generated when electrically charged particles move through matter or a vacuum. Alternatively, it can also be produced by oscillating magnetic and electric disturbances.

Let's delve deeper into the key aspects of electromagnetic radiation:

Energy from Charged Particles: Electromagnetic radiation is generated when electrically charged particles, such as electrons, move through a medium or empty space. These particles carry energy as they travel, creating a wave-like pattern of electric and magnetic fields.

Electric and Magnetic Fields:Electromagnetic radiation consists of electric and magnetic fields. These fields are intimately connected and perpendicular to each other, with a 90-degree angle. As the combined waves propagate through space, they move perpendicular to the electric and magnetic oscillations occurring during the disturbance.

Diverse Forms of Electromagnetic Radiation: Electromagnetic radiation encompasses a vast spectrum of energy, ranging from low-energy radio waves to high-energy gamma rays. Some common forms of electromagnetic radiation include microwaves, television waves, radio waves, infrared radiation, visible light, ultraviolet radiation, X-rays, and gamma rays. Each form has different wavelengths and energy levels, resulting in unique properties and applications.

Transverse Waves: Electromagnetic radiation travels as transverse waves, meaning that the oscillations occur perpendicular to the direction of wave propagation. This characteristic allows electromagnetic radiation to traverse space, enabling it to propagate through a vacuum, unlike other types of waves.

Properties of Electromagnetic Radiation

Photons: Electromagnetic radiation is emitted as discrete packets of energy called photons. These photons carry light energy and travel at the constant speed of light.

Quantized Harmonic Waves: Electromagnetic radiation can be described as quantized harmonic waves. These waves exhibit specific frequencies and energy levels.

Categorization by Wavelength: Electromagnetic radiation is grouped into different categories based on its wavelength within the electromagnetic spectrum. Each category has distinct properties and applications.

Perpendicular Electric and Magnetic Fields: Electromagnetic waves consist of perpendicular electric and magnetic fields. These fields oscillate in directions that are perpendicular to each other and to the direction of wave propagation.

Wavelength, Amplitude, and Frequency: Electromagnetic radiation exhibits properties such as wavelength, amplitude, and frequency. Wavelength (λ) represents the distance between two adjacent points in phase, while frequency determines the number of wave cycles per second. Amplitude refers to the maximum displacement of the wave from its equilibrium position.

Travel through Empty Space: Unlike other types of waves, electromagnetic radiation can travel through empty space. It does not require a medium such as a solid, liquid, or gas for propagation.

Constant Speed of Light: The speed of light in a vacuum, denoted as "c," is a fundamental constant of approximately 2.99792458 x 10⁸ metres per second. This speed remains constant for all forms of electromagnetic radiation.

Understanding the properties of electromagnetic radiation allows us to comprehend its behaviour, interactions with matter, and various applications across scientific disciplines and everyday life.

Types of Electromagnetic Radiation

Gamma-rays

Gamma rays have the highest frequency and photon energy in the electromagnetic spectrum. They have extremely short wavelengths and are associated with nuclear processes and high-energy particle interactions.

Read More: Gamma Rays

X-rays

X-rays have frequencies and photon energies slightly lower than gamma rays. They are widely used in medical imaging, security screening, and industrial applications due to their ability to penetrate materials and reveal internal structures.

Read More: X-rays

Ultraviolet (UV) Rays

Ultraviolet rays have higher frequencies and photon energies than visible light. They are emitted by the Sun and play a crucial role in biological processes, such as vitamin D synthesis and triggering chemical reactions in the atmosphere.

Read More: Ultraviolet Rays

Visible Light:

Visible light is the portion of the electromagnetic spectrum visible to the human eye. Visible light is essential for vision. It has a range of frequencies and photon energies that allow us to perceive different colours.
Read More: Visible Light

Infrared (IR) Rays

Infrared rays have lower frequencies and photon energies than visible light. They are associated with thermal radiation and are commonly used in night vision, remote sensing, and infrared spectroscopy applications.

Read More: Infrared Rays

Radio Waves

Radio waves have the lowest frequencies and photon energies in the electromagnetic spectrum. They are used for communication, broadcasting, and radar systems. Different portions of the radio wave spectrum are allocated for various applications, including AM and FM radio, television, and mobile communication.

Read More: Radio Waves

Microwaves

Microwaves have slightly higher frequencies and photon energies than radio waves. They are commonly used in microwave ovens, satellite communication, and wireless technologies.

Read More: Microwaves

Understanding the electromagnetic spectrum allows us to explore the diverse range of electromagnetic radiation and its applications.

Discover the key differences between infrared, visible, and ultraviolet radiation in this video tutorial!

Electromagnetic Radiation Characteristics

Understanding the characteristics of electromagnetic waves is crucial to comprehending the behaviour and applications of electromagnetic waves. Let's explore these characteristics in more detail:

Wavelength

Wavelength (λ) represents the distance between successive crests or troughs of a wave. It is the length of one complete cycle of oscillation. Wavelength and frequency (ν) are related by the equation c = λν, where 'c' is the speed of light. Shorter wavelengths correspond to higher frequencies and higher energy levels.

Amplitude

Amplitude refers to the maximum displacement of a wave from its equilibrium position. It represents the distance from the middle of the wave to the crest or trough. Amplitude provides information about the brightness or intensity of a wave relative to other waves. Larger amplitudes indicate higher energy levels, while smaller amplitudes correspond to lower energy levels.

Frequency

Frequency is the number of wave cycles that occur per second, measured in Hertz (Hz) or cycles per second. It determines how many times a wave oscillates within a given time frame. Frequency (ν) and energy (E) is directly proportional, as indicated by the equation E = hν, where 'h' is Planck's constant (6.62607 x 10⁻³⁴). Higher frequencies correspond to higher energy levels.

Period

Period (T) represents a wave's total time to complete one full cycle or travel one wavelength. It is the reciprocal of frequency, given by T = 1/ν. The period provides information about the time characteristics of a wave.

Velocity

In electromagnetic radiation, velocity is expressed as the product of wavelength and frequency, given by Velocity = λν. For electromagnetic waves propagating in a vacuum, the velocity is equal to the speed of light, which is approximately 186,282 miles per second or 2.99 x 10 ⁸ metres per second (m/s).

Understanding these characteristics of electromagnetic waves allows us to interpret and utilise their behaviour across a wide range of scientific, technological, and everyday applications.

Electromagnetic Spectrum

The electromagnetic spectrum is the range of frequencies of EM radiations along with their associated wavelengths and photon energies. It includes various types of waves, such as gamma rays, X-rays, ultraviolet rays, infrared rays, radio waves, and microwaves. The electromagnetic spectrum spans a wide range of frequencies, corresponding to different wavelengths and photon energy levels. Gamma rays have the highest frequencies and energy levels, while radio waves have the lowest. Each segment of the spectrum exhibits unique properties and interactions with matter. Electromagnetic waves, including those within the spectrum, propagate at the speed of light in a vacuum, approximately 299,792,458 metres per second (m/s).

Electromagnetic Theory

The field of electromagnetism emerged from the realisation that electricity and magnetism are interconnected phenomena. One pivotal moment in this journey was the groundbreaking experiment conducted by Hans Christian Oersted, a Danish physicist, in 1820. Oersted observed that when a compass needle was placed near a current-carrying conductor, it deflected from its original position, revealing a direct connection between electric currents and magnetic fields. This revelation laid the foundation for the development of electromagnetism as a unified field of study and showcased the fundamental principle known as the right hand thumb rule, which determines the direction of the magnetic field around a current-carrying conductor.

The contributions of Scottish physicist James Clerk Maxwell further revolutionised the field of electromagnetism. In 1873, Maxwell formulated a set of equations, known as Maxwell's equations, that expanded upon the existing laws of electricity and magnetism. This comprehensive theory of electromagnetism provided a mathematical framework for understanding the behaviour of electromagnetic fields. Maxwell's equations demonstrated the interconnectedness of electric and magnetic fields, revealing that they can propagate through space as electromagnetic waves.

Maxwell's theory not only mathematically derived the existence of electromagnetic waves but also predicted that these waves travel at the speed of light. This led to Maxwell proposing that light itself is an electromagnetic wave, unifying the fields of optics and electromagnetism. This groundbreaking insight established a profound connection between light and the broader electromagnetic spectrum.

Key Principles of Electromagnetic Theory

1. Interactions of Electrically Charged Particles: Electromagnetic theory examines how electrically charged particles interact with one another and with magnetic fields. This interaction forms the basis for understanding various electromagnetic phenomena.

2. Magnetic Poles and Electric Charges: Similar to electric charges, magnetic poles exist in pairs and exhibit both attraction and repulsion. Opposite magnetic poles attract each other, while like poles repel. This behaviour parallels the interactions observed between electric charges.

3. Inverse Square Law: The force of attraction or repulsion between two electric charges is inversely proportional to the square of the distance between them. As the distance between charges increases, the force decreases, following the inverse square law.

4. Relationship between Electric and Magnetic Fields: An electric field in motion generates a magnetic field, and vice versa. This dynamic relationship between electric and magnetic fields is fundamental to electromagnetism and is described by Maxwell's equations.

5. Magnetic Field Produced by Electric Current: When an electric current flows through a wire, it creates a magnetic field around it. The direction of the magnetic field depends on the direction of the electric current. This principle forms the basis for various electromagnetic devices and technologies, including electromagnets and electric motors.

Watch the video to explore Oersted's experiment, the compass needle deflection, and the power of the right hand thumb rule!

Understanding the principles of electromagnetic theory allows us to explain and predict a wide range of phenomena, from the behaviour of magnets to the generation and transmission of electrical energy. It provides the foundation for technologies such as generators, transformers, and wireless communication systems, enabling advancements in various scientific and engineering fields.

Frequently Asked Questions - FAQs

What is electromagnetic radiation?

Electromagnetic radiation is a form of energy that is produced by the movement of electrically charged particles or oscillating electric and magnetic fields. It includes a wide range of waves, such as radio waves, microwaves, infrared, visible light, ultraviolet, X-rays, and gamma rays.

What are the properties of electromagnetic radiation?

Electromagnetic radiation has several properties, including the ability to travel through empty space, constant speed of light, different wavelengths and frequencies, and a range of energy levels.

What are the types of electromagnetic radiation?

The types of electromagnetic radiation include gamma rays, X-rays, ultraviolet (UV) rays, visible light, infrared (IR) rays, microwaves, and radio waves. Each type has distinct properties and applications.

What are the characteristics of electromagnetic radiation?

Electromagnetic radiation is characterised by properties such as wavelength, frequency, amplitude, and energy. Different types of electromagnetic radiation have varying wavelengths. The frequency and energy increase as the wavelength decreases.

What is the electromagnetic spectrum?

The electromagnetic spectrum refers to the entire range of electromagnetic radiation ranging from high-energy gamma rays to low-energy radio waves, with visible light occupying a small portion in the middle. The electromagnetic spectrum is essential for understanding and utilising different forms of electromagnetic radiation.

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Understanding Electromagnetic Radiation - Properties, Types, and Characteristics

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Explore electromagnetic radiation, its properties, types, and characteristics. Learn about the electromagnetic spectrum, electromagnetic theory and watch captivating videos.

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What are rainbows? #Rainbow Facts for kids

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What is a rainbow?

Rainbows are a phenomenon we see when we line up in the right direction with the sun and water droplets in the air. Rainbows are the product of light refraction and reflection. Refraction is the bending of light by water, air, or gases. Reflection is the return of light after being bounced off a surface.

How are rainbows created?

The first step in the creation of a rainbow is when light enters a water droplet and becomes refracted. Next, it is reflected by the back of the droplet. When the reflected light leaves the droplet, it is refracted again, but at multiple angles. With the help of dispersion, we are able to see the many colors of the rainbow. Dispersion is the spreading of white light into its full spectrum of wavelengths.

What allows us to see the colors of the rainbow?

The colors of the rainbow relate to electromagnetic radiation. Electromagnetic radiation is a form of energy that we see all around us and allows us to see the rainbow. Electromagnetic radiation has a spectrum of the different types of wavelengths that are seen as the colors.

Why are the colors of the rainbow in a certain order?

The electromagnetic spectrum includes the many different wavelengths that are each reflected at a different angle. This is why some colors of the rainbow appear to be longer than others. Red, the longest color of the rainbow, has the longest wavelength. Violet has the shortest wavelength, so it appears at the bottom of the rainbow.