English Reading Series Part 2 Light (This article is only suitable for middle school students to read technical texts)
What: Physics Physics
Text: 1115 words
Title: Light (Optics): Definition, Units & Sources
Title: Light (Optical): Definitions, Units, and Lights
Understanding light allows us to understand how we see, perceive color and even correct
our vision with lenses. The field of optics refers to the study of light.
Understanding light allows us to understand how we see, perceive colors, and even correct our vision with lenses. The field of optics refers to the study of light.
<h1 class="pgc-h-arrow-right" data-track="10" >What Is Light? </h1>
In everyday speech, the word "light" often really means visible light, which is the type perceived by the human eye. However, light comes in many other forms, the vast majority of which humans cannot see.
In everyday parlance, the word "light" usually really means visible light, which is the type perceived by the human eye. However, there are many other forms of light, the vast majority of which are invisible to humans.
The source of all light is electromagnetism, the interplay of electric and magnetic fields that permeate space. Light waves are a form of electromagnetic radiation; the terms are interchangeable. Specifically, electromagnetic waves are self-propagating oscillations in electric and magnetic fields.
The source of all light is the electromagnetic force, the interaction of electric and magnetic fields that permeate space. Light waves are a form of electromagnetic radiation; these terms are interchangeable. Specifically, electromagnetic waves are self-propagating oscillations in electric and magnetic fields.
In other words, light is a vibration in an electromagnetic field. It passes through space as a wave.
In other words, light is a vibration in an electromagnetic field. It travels through space in the form of waves.
Knowledge Points Knowledge points
The speed of light in a vacuum is 3 × 10^8 m/s, the fastest speed in the universe!
The speed of light in a vacuum is 3×10^8 = m/s, the fastest speed in the universe!
It is a unique and bizarre feature of our existence that nothing travels faster than light. And although all light, whether visible or not, travels at the same speed, when it encounters matter, it slows down. Because light interacts with matter (which doesn't exist in a vacuum), the denser the matter, the slower it travels.
Nothing travels faster than the speed of light, and it is a unique and bizarre feature of our existence. Although all light, visible or not, travels at the same speed, it slows down when it encounters matter. Because light interacts with matter (which does not exist in a vacuum), the denser the matter, the slower it spreads.
Light's interactions with matter hint at another of its important characteristics: its particle nature. One of the strangest phenomena in the universe, light is actually two things at once: a wave and a particle. This wave-particle duality makes studying light somewhat dependent on context.
The interaction of light with matter hints at another important feature of it: its particle properties. As one of the strangest phenomena in the universe, light is actually two things at the same time: waves and particles. This wave-particle duality makes the study of light depend in part on the description of the context.
At times, physicists find it most helpful to think of light as a wave, applying to it much of the same mathematics and properties that describe sound waves and other mechanical waves. In other cases, modeling light as a particle is more appropriate, for instance when considering its relationship to atomic energy levels or the path it will take as it reflects off a mirror.
Sometimes, physicists find it most helpful to think of light as waves, applying many of the same math and properties that describe sound waves and other mechanical waves to it. In other cases, modeling light as a particle is more appropriate, such as when considering its relationship to atomic energy levels or the path it will take when reflected from a mirror.
<h1 class="pgc-h-arrow-right" data-track="29" > The Electromagnetic Spectrum</h1>
If all light, visible or not, is technically the same thing – electromagnetic radiation – what distinguishes one type from another? Its wave properties.
If all light, visible or not, is technically the same thing — electromagnetic radiation — what distinguishes one type from another? The characteristics of its waves.
Electromagnetic waves exist in a spectrum of different wavelengths and frequencies. As a wave, light's speed follows the wave speed equation, where the speed is equal to the product of wavelength and frequency:
Electromagnetic waves exist in spectrums of different wavelengths and frequencies. As waves, the speed of light follows the wave velocity equation, where velocity is equal to the product of wavelength and frequency:
V = λf
In this equation, v is wave velocity in meters per second (m/s), λ is wavelength in meters (m) and f is frequency in hertz (Hz).
In this equation, v is the wave velocity in meters per second (m/s), λ is the wavelength in meters (m), and f is the frequency in hertz (Hz).
In the case of light, this can be rewritten with the variable c for the speed of light in a vacuum:
In the case of light, this can be rewritten with the variable c of the speed of light in a vacuum:
c=λf
<h1 class="pgc-h-arrow-right" data-track="40" > Know-kill points</h1>
c is a special variable representing the speed of light in a vacuum. In other media (materials), light's speed can be expressed as a fraction of c.
c is a special variable that represents the speed of light in a vacuum. In other media (materials), the speed of light can be expressed as a fraction of c.
This relationship implies that light can have any combination of wavelength or frequency, so long as the values are inversely proportional and their product equals c. In other words, light can have a large frequency and a small wavelength, or vice versa.
This relationship means that light can have any combination of wavelengths or frequencies, as long as these values are inversely proportional and their product is equal to c. In other words, light can have large frequencies and small wavelengths, and vice versa.
At different wavelengths and frequencies, light has different properties. So, scientists have divided up the electromagnetic spectrum into segments representing these properties. For example, very high frequencies of electromagnetic radiation, like ultraviolet rays, X-rays or gamma rays, are very energetic – enough to penetrate and harm body tissues. Others, like radio waves, have very low frequencies but high wavelengths, and they pass through bodies unimpeded all the time. (Yes, the radio signal carrying your favorite DJ's tracks through the air to your device is a form of electromagnetic radiation – light!)
At different wavelengths and frequencies, light has different properties. As a result, scientists divide the electromagnetic spectrum into sections that represent these characteristics. For example, very high frequencies of electromagnetic radiation, such as ultraviolet, X-rays or gamma rays, are very energetic – enough to penetrate and damage body tissues. Others, such as radio waves, have low frequencies but high wavelengths, and they are constantly moving through the body unhindered. (Yes, the radio signal that transmits your favorite DJ tracks through the air to your device is an electromagnetic radiation – light!) ）
The forms of electromagnetic radiation from longer wavelengths/lower frequencies/low energy to shorter wavelengths/higher frequencies/high energy are:
The forms of electromagnetic radiation from longer wavelengths/lower frequencies/low energies to shorter wavelengths/higher frequencies/high energies are:
· Radio waves
· Microwaves microwaves
· Infrared waves infrared
· Visible light visible light
· Ultraviolet light UV light
· X-rays X-rays
· Gamma rays gamma rays
<h1 class="pgc-h-arrow-right" data-track="57" > The Visible Spectrum visible spectrum</h1>
The visible light spectrum spans wavelengths from 380-750 nanometers (1 nanometer equals 10-9 meters – one-billionth of a meter, or about the diameter of a hydrogen atom). This part of the electromagnetic spectrum includes all the colors of the rainbow – red, orange, yellow, green, blue, indigo and violet – that are visible to the eye.
The wavelength range of the visible spectrum is 380-750 nanometers (1 nanometer equals 10-9 meters, which is equivalent to one billionth of a meter, or about the diameter of a hydrogen atom). This part of the electromagnetic spectrum includes all the colors of the rainbow visible to the naked eye — red, orange, yellow, green, blue, indigo, and purple.
Because red has the longest wavelength of the visible colors, it also has the smallest frequency and thus the lowest energy. The opposite is true for blues and violets. Because the energy of the colors is not the same, neither is their temperature. In fact, the measurement of these temperature differences in visible light led to the discovery of the existence of other light invisible to humans.
Since red has the longest wavelength among visible colors, it also has the lowest frequency and therefore the lowest energy. Blue and violet are the opposite. Because the energy of the colors is not the same, their temperature is also different. In fact, by measuring these temperature differences in visible light, the presence of other lights that are invisible to humans has been discovered.
In 1800, Sir Frederick William Herschel devised an experiment to measure the difference in temperatures for different colors of sunlight that he separated using a prism. While he indeed found different temperatures in different color regions, he was surprised to see the hottest temperature of all recorded on the thermometer just beyond the red, where there appeared to be no light at all. This was the first evidence that more light existed than humans could see. He named the light in this region infrared, which translates directly to "below red."
In 1800, Sir Frederick William Herschel devised an experiment to measure the temperature difference between the different colors of sunlight he separated using prisms. While he did find different temperatures in different color areas, he was surprised to find that the hottest temperature recorded on the thermometer was just outside the red, where there seemed to be no light at all. This is the first evidence that there is more light than humans can see. He named the light in this area Infrared, which translates directly as "below red."
White light, usually what a standards light bulb gives off, is a combination of all the colors. Black, in contrast, is the absence of any light – not really a color at all!
White light, usually the light emitted by a standard bulb, is a combination of all colors. In contrast, black does not have any light – it is not a color at all!
<h1 class="pgc-h-arrow-right" data-track="66" > Wave Fronts and Rays wavefronts and rays</h1>
Optics engineers and scientists consider light in two different ways when determining how it will bounce, combine and focus. Both descriptions are needed to predict the final intensity and location of light as it focuses through lenses or mirrors.
Optical engineers and scientists consider light in two different ways when determining how it is reflected, combined, and focused. When light is focused through a lens or mirror, both descriptions are needed to predict the final intensity and position of the light.
In one case, opticians look at light as series of transverse wave fronts, which are repeating sinusoidal or S-shaped waves with crests and troughs. This is the physical optics approach, as it uses the wave nature of light to understand how light interacts with itself and leads to patterns of interference, the same way that waves in water can intensify or cancel one another out.
In one case, optical experts think of light as a series of lateral wavefronts that are repetitive sine waves or S-shaped waves with peaks and troughs. This is a physical optical approach because it uses the volatility of light to understand how light interacts with itself and leads to interference patterns, just as waves in water can enhance or cancel each other out.
Physical optics began after 1801 when Thomas Young discovered light's wave properties. It helps to explain the workings of such optical instruments as diffraction gratings, which separate the spectrum of light into its component wavelengths, and polarization lenses, which block certain wavelengths.
Physical optics began in 1801, when Thomas Young discovered the fluctuating properties of light. It helps explain how optical instruments such as diffraction gratings and polarized lenses (blocking certain wavelengths) work, which divides the spectrum into its constituent wavelengths.
The other way to think of light is as a ray, a beam following a straight-line path. A ray is drawn as a straight line emanating from a light source and indicating the direction in which light travels. Expressing light as a ray is useful in geometric optics, which relates more to the particle nature of light.
Another way of treating light as light, a beam of light along a straight path. Rays are drawn as straight lines emitted from a light source and indicating the direction in which the light travels. Representing light as light is useful in geometric optics, which has more to do with the particle properties of light.
Drawing ray diagrams showing the path of light is critical to designing such light-focusing tools as lenses, prisms, microscopes, telescopes and cameras. Geometric optics has been around for longer than physical optics – by 1600, the era of Sir Isaac Newton, corrective lenses for vision were commonplace.
Drawing a ray map showing the optical path is essential for designing light-focusing tools such as lenses, prisms, microscopes, telescopes, and cameras. Geometric optics existed longer than physical optics—by 1600, during the time of Sir Isaac Newton, vision-correcting lenses were commonplace.
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