光通量的下標為什麼是v（光光學:定義）

2023-04-28 18:56:35 11

英語閱讀系列第2篇光 （本文僅適合中學生閱讀科技類文本）

內容: 物理 Physics

正文: 1115個單詞 Text: 1115 words

Title: Light (Optics): Definition, Units & Sources

標題: 光（光學）:定義、單位和光源

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.

了解光可以讓我們了解我們如何看待、感知顏色，甚至用鏡片矯正我們的視力。光學領域是指對光的研究。

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.

在日常用語中，「光」這個詞通常真正意味是可見光 ，這是人眼所感知的類型。 然而，光有許多其他形式，其中絕大多數是人類無法看到的。

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.

所有光的來源是電磁力，即滲透空間的電場和磁場的相互作用。 光波是電磁輻射的一種 形式 ； 這些術語可以互換。 具體而言，電磁波是電場和磁場中的自傳播振蕩。

In other words, light is a vibration in an electromagnetic field. It passes through space as a wave.

換句話說，光是電磁場中的振動。 它以波的形式穿過空間。

Knowledge Points 知識點

The speed of light in a vacuum is 3 × 10^8 m/s, the fastest speed in the universe!

真空中的光速為3×10^8 = m/s，是宇宙中最快的速度！

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.

沒有什麼比光速傳播得更快，這是我們存在的一個獨特而奇異的特徵。儘管所有的光，無論是否可見，都以相同的速度傳播，但當它遇到物質時，它會變慢。因為光與物質（真空中不存在）相互作用，物質越密，傳播越慢。

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.

光與物質的相互作用暗示了它的另一個重要特徵：它的粒子性質。作為宇宙中最奇怪的現象之一，光實際上同時是兩種東西：波和粒子。這種波粒二象性使得研究光在某種程度上取決於上下文的描述。

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.

有時，物理學家發現將光視為波最有幫助，將描述聲波和其他機械波的許多相同數學和屬性應用於它。在其他情況下，將光建模為粒子更合適，例如在考慮它與原子能級的關係或它從鏡子反射時將採用的路徑時。

If all light, visible or not, is technically the same thing – electromagnetic radiation – what distinguishes one type from another? Its wave properties.

如果所有的光，無論可見與否，在技術上都是同一種東西——電磁輻射——是什麼使一種類型與另一種類型區別開來？ 其波的特性。

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:

電磁波存在於不同波長和頻率的頻譜中。 作為波，光速遵循波速方程，其中速度等于波長和頻率的乘積：

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).

在此等式中， v 是以米每秒 (m/s) 為單位的波速， λ 是以米 (m) 為單位的波長， f 是以赫茲 (Hz) 為單位的頻率。

In the case of light, this can be rewritten with the variable ​c​ for the speed of light in a vacuum:

在光的情況下，這可以用真空中光速的變量 c 重寫：

c=λf

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是代表真空中光速的特殊變量。在其他介質（材料）中，光速可以表示為c的一小部分。

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.

這種關係意味著光可以有任何波長或頻率的組合，只要這些值成反比並且它們的乘積等於 c。換句話說，光可以具有大頻率和小波長，反之亦然。

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!)

在不同的波長和頻率下，光具有不同的特性。因此，科學家們將電磁頻譜劃分為代表這些特性的部分。例如，非常高頻率的電磁輻射，如紫外線、X 射線或伽馬射線，非常有能量——足以穿透和傷害身體組織。其他的，比如無線電波，頻率很低，但波長很高，它們一直在不受阻礙地穿過身體。 （是的，通過空氣將您最喜歡的 DJ 曲目傳送到您的設備的無線電信號是一種電磁輻射 - 光！）

The forms of electromagnetic radiation from longer wavelengths/lower frequencies/low energy to shorter wavelengths/higher frequencies/high energy are:

從較長波長/較低頻率/低能量到較短波長/較高頻率/高能量的電磁輻射形式是：

· Radio waves 無線電波

· Microwaves 微波

· Infrared waves 紅外線

· Visible light 可見光

· Ultraviolet light 紫外光線

· X-rays X射線

· Gamma rays 伽馬射線

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.

可見光譜的波長範圍為 380-750 納米（1 納米等於 10-9 米 ，相當於一米的十億分之一，或大約為氫原子的直徑）。這部分電磁波譜包括肉眼可見的彩虹的所有顏色——紅色、橙色、黃色、綠色、藍色、靛藍色和紫色。

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.

由於紅色在可見色中波長最長，因此頻率也最低，因此能量最低。藍色和紫羅蘭色則相反。因為顏色的能量不一樣，它們的溫度也不一樣。事實上，通過測量可見光中的這些溫差，人們發現了人類不可見的其他光的存在。

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."

1800年，弗雷德裡克·威廉·赫歇爾爵士設計了一項實驗來測量他使用稜鏡分離的不同顏色陽光的溫度差異。雖然他確實在不同的顏色區域發現了不同的溫度，但他驚訝地發現溫度計上記錄的最熱溫度正好在紅色之外，那裡似乎根本沒有光。這是第一個證明存在比人類所能看到的更多的光的證據。他將這個區域的光命名為 紅外線 ，直接翻譯為「低於紅色」。

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!

白光，通常是標準燈泡發出的光，是所有顏色的組合。相比之下，黑色是不存在任何光線的——根本就不是一種顏色！

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.

光學工程師和科學家在確定光如何反射、組合和聚焦時會以兩種不同的方式考慮光。當光通過透鏡或鏡子聚焦時，需要這兩種描述來預測光的最終強度和位置。

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.

在一種情況下，光學專家將光視為一系列橫向波陣面，這些波陣面是具有波峰和波谷的重複正弦波或 S 形波。這是物理光學方法，因為它利用光的波動性來了解光如何與其自身相互作用並導致幹涉模式，就像水中的波浪可以增強或相互抵消一樣。

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.

物理光學始於 1801 年，當時 Thomas Young 發現了光的波動特性。它有助於解釋諸如衍射光柵和偏振透鏡（阻擋某些波長）等光學儀器的工作原理，衍射光柵將光譜分成其組成波長。

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.

另一種將光視為光線的方式，即沿著直線路徑的光束。光線被繪製為從光源發出並指示光傳播方向的直線。將光表示為光線在幾何光學 中很有用，這更多地與光的粒子性質有關。

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.

繪製顯示光路的射線圖對於設計諸如透鏡、稜鏡、顯微鏡、望遠鏡和相機等光聚焦工具至關重要。幾何光學比物理光學存在的時間更長——到 1600年，艾薩克·牛頓爵士時代，視力矯正鏡片已經司空見慣。

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