📚 Understanding Ultraviolet Radiation: The 357 nm Wavelength | 理解紫外线辐射：357纳米波长
Electromagnetic radiation is all around us, from the radio waves that carry music to the X-rays used in hospitals. One particularly interesting part of the electromagnetic spectrum is ultraviolet (UV) radiation, which sits between visible light and X-rays. In this article, we will focus on a specific UV wavelength – 357 nanometres (nm) – and explore what it is, why it matters, and how we can protect ourselves from it.
电磁辐射无处不在：从传递音乐的无线电波，到医院使用的X射线。在电磁波谱中，一个特别有趣的区域是紫外线（UV），它位于可见光和X射线之间。本文将聚焦一个特定的紫外线波长——357纳米（nm），探讨它是什么、为什么重要，以及我们如何保护自己免受其伤害。
1. What is Electromagnetic Radiation? | 什么是电磁辐射？
l travel at the same speed in a vacuum: 3.0 × 10⁸ m/s, commonly called the speed of light.
电磁波是由振荡的电场和磁场产生的横波。它们在真空中的传播速度相同，均为3.0 × 10⁸ m/s，通常称为光速。
The energy carried by an electromagnetic wave depends on its frequency and wavelength. The wave equation c = f × λ links these quantities, where c is the speed of light, f is frequency, and λ (lambda) is wavelength.
电磁波携带的能量与其频率和波长有关。波方程 c = f × λ 联系了这些量，其中c是光速，f是频率，λ（lambda）是波长。
2. The Electromagnetic Spectrum | 电磁波谱
The electromagnetic (EM) spectrum is the full range of electromagnetic waves, ordered by wavelength and frequency. From long wavelength to short wavelength, the main types are: radio waves, microwaves, infrared, visible light, ultraviolet, X-rays, and gamma rays.
电磁波谱是电磁波按波长和频率排列的完整范围。从长波长到短波长，主要类型有：无线电波、微波、红外线、可见光、紫外线、X射线和伽马射线。
Ultraviolet sits between visible violet light and X-rays, with wavelengths roughly from 400 nm down to 10 nm. Because its wavelength is shorter than visible light, UV has higher frequency and higher energy per photon.
紫外线位于可见光中的紫光和X射线之间，波长大约从400 nm到10 nm。由于它比可见光波长短，所以紫外线具有更高的频率和更高的单光子能量。
3. What is Ultraviolet Radiation? | 什么是紫外线辐射？
Ultraviolet radiation is invisible to the human eye. It is produced by the Sun, as well as by artificial sources such as tanning lamps and black lights. UV can cause chemical reactions and can damage living tissue, which is why we need to be careful with exposure.
紫外线是人眼不可见的辐射。它由太阳以及人工光源（如美黑灯和紫外灯）产生。紫外线能引发化学反应，也能损伤生物组织，因此我们必须小心接触。
7 nm is still ultraviolet, but it is comparatively close to visible violet light (about 380–450 nm).
357 nm这个特定波长位于UVA区域，我们将在下一小节解释。波长为357 nm的波仍然属于紫外线，但它相对接近可见光中的紫光（约380–450 nm）。
4. The UV Subtypes: UVA, UVB, UVC | 紫外线的亚型：UVA、UVB、UVC
Ultraviolet radiation is divided into three main bands based on wavelength:
紫外线根据波长分为三个主要波段：
| Band | Wavelength (nm) | Example |
| UVA | 400 – 315 | 357 nm is in this range |
| UVB | 315 – 280 | Causes sunburn |
| UVC | 280 – 100 | Absorbed by the ozone layer |
UVA makes up about 95% of the Sun's UV radiation that reaches Earth's surface. UVC is extremely harmful but is almost entirely absorbed by the ozone layer. UVB is only partially absorbed and is responsible for tanning and burning.
UVA约占到达地球表面的太阳紫外线的95%。UVC极其有害，但几乎完全被臭氧层吸收。UVB只被部分吸收，是导致皮肤变黑和晒伤的原因。
5. The Energy of a 357 nm Photon | 357纳米光子的能量
The energy of a single photon can be calculated from its wavelength using the formula:
单个光子的能量可由其波长通过以下公式计算：
E = hc/λ
where h is Planck' ngth in metres. For λ = 357 nm, first convert nanometres to metres: 357 nm = 357 × 10⁻⁹ m.
其中h是普朗克常数（6.63 × 10⁻³⁴ J·s），c是光速（3.0 × 10⁸ m/s），λ是以米为单位的波长。对于λ = 357 nm，先将纳米转换为米：357 nm = 357 × 10⁻⁹ m。
E = (6.63 × 10⁻³⁴ × 3.0 × 10⁸) ÷ (357 × 10⁻⁹) ≈ 5.57 × 10⁻¹⁹ J
This energy is about 3.48 electronvolts (eV). It is more energetic than visible photons, which range roughly from 1.8 eV to 3.1 eV. This extra energy allows UV light to break chemical bonds and cause damage to DNA.
这个能量约为3.48电子伏特（eV）。它比可见光光子（约1.8 eV到3.1 eV）能量更高。这份额外的能量使紫外线能够打断化学键，并对DNA造成损伤。
6. Sources of Ultraviolet Radiation | 紫外线的来源
The Sun is the most powerful natural source of UV radiation, but not all of its UV reaches the ground. The atmosphere blocks almost all UVC, most UVB, and a large fraction of UVA. However, on a clear day at high altitude, more UV reaches the surface.
太阳是紫外线最强的自然来源，但并非所有紫外线都能到达地面。大气层几乎阻挡了所有UVC，大部分UVB和很大一部分UVA。然而，在晴朗的高海拔地区，到达表面的紫外线会更多。
Artificial sources include mercury-vapour lamps, tanning salons, welding torches, and "black lights" used in entertainment and forensic science. Some fluorescent lamps also emit small amounts of UV, though it is converted to visible light by the phosphor coating.
人工光源包括汞蒸气灯、美黑沙龙、焊弧以及娱乐和法医科学中使用的“黑光灯”。一些荧光灯也会发出少量紫外线，不过这些紫外线会被荧光粉涂层转换为可见光。
7. Positive Effects of UV: Vitamin D and Therapy | 紫外线的好处：维生素D与治疗
Not all UV is harmful. When human skin is exposed to UVB radiation, the body synthesises vitamin D, which is essential for calcium absorption and healthy bones. Moderate sun exposure helps maintain adequate vitamin D levels.
并非所有紫外线都有害。当人类皮肤暴露于UVB辐射时，人体会合成维生素D，这对钙吸收和骨骼健康至关重要。适度的阳光照射有助于维持足够的维生素D水平。
UV is also used in medicine. Phototherapy with UVA or narrowband UVB can treat skin conditions such as psoriasis and eczema. Ultraviolet light can also be used to sterilise medical equipment and disinfect water, because it destroys the DNA of microorganisms.
紫外线也用于医学。使用UVA或窄谱UVB的光疗可以治疗银屑病和湿疹等皮肤病。紫外线还可用于消毒医疗设备和净化水，因为它能破坏微生物的DNA。
8. Harmful Effects of UV | 紫外线的危害
Overexposure to UV radiation is dangerous. The energy from UV photons can be absorbed by DNA molecules, causing mutations that may lead to skin cancer. UVB is especially associated with sunburn, while UVA penetrates deeper into the skin and accelerates ageing.
过度暴露于紫外线辐射是危险的。紫外线光子的能量会被DNA分子吸收，导致突变，进而可能引发皮肤癌。UVB与晒伤尤其相关，而UVA穿透皮肤更深，会加速老化。
Eyes are also vulnerable. Without proper eye protection, long-term UV exposure can cause cataracts and photokeratitis. Consequently, sunglasses with UV blocking are essential when spending time outside.
眼睛也同样脆弱。如果没有适当的眼部防护，长期暴露于紫外线会导致白内障和光性角膜炎。因此，在户外活动时，佩戴能阻挡紫外线的太阳镜非常重要。
9. The Ozone Layer and UV Protection | 臭氧层与紫外线防护
The ozone layer in the stratosphere acts as a natural sunscreen. Ozone molecules absorb most UVC and a significant part of UVB, preventing them from reaching Earth's surface. Ozone depletion, mainly caused by chlorofluorocarbons (CFCs), allows more UVB to pass through.
平流层中的臭氧层充当天然防晒霜。臭氧分子吸收大部分UVC和相当一部分UVB，阻止它们到达地球表面。臭氧层损耗，主要由氯氟烃（CFCs）导致，会让更多UVB透过。
Practical protection measures include using broad-spectrum sunscreen (SPF 30 or higher), wearing protective clothing and hats, and avoiding direct Sun exposure between 10 a.m. and 4 p.m. when UV intensity is highest.
实际的防护措施包括使用广谱防晒霜（SPF 30或更高）、穿着防护衣物和帽子，并避免在上午10点到下午4点之间直接暴露于阳光下，因为此时紫外线强度最高。
10. Applications of UV in Everyday Life | 紫外线在日常生活中的应用
UV radiation has many practical uses:
紫外线有许多实际用途：
Sterilisation: UVC lamps are used in hospitals, water plants, and food packaging to kill bacteria and viruses.
杀菌：UVC灯用于医院、水厂和食品包装中，以杀灭细菌和病毒。
Fluorescence: Many substances glow when exposed to UV. Security markers and anti-counterfeit currency use invisible UV-fluorescent inks.
荧光：许多物质在紫外线照射下会发光。防伪标记和防伪货币使用不可见的紫外荧光油墨。
Forensics: UV light reveals blood stains, fingerprints, and other evidence that is invisible under ordinary light.
法医学：紫外线可以显现普通光下不可见的血迹、指纹和其他证据。
UV curing: Dental composite fillings and some adhesives harden quickly under UV light.
光固化：牙科复合树脂填充物和一些粘合剂在紫外线下能快速硬化。
The 357 nm wavelength is particularly useful in fluorescence applications because it is absorbed by many materials that then re-emit visible light.
357 nm波长在荧光应用中特别有用，因为许多材料会吸收该波长的光，然后重新发射出可见光。
11. Detecting and Measuring UV | 紫外线的检测与测量
UV radiation cannot be seen, so we need instruments to detect it. Photodiodes and UV sensors use materials that produce an electrical signal when exposed to UV. Simple detectors use paper coated with chemicals that change colour.
紫外线看不见，因此我们需要仪器来检测它。光电二极管和紫外线传感器使用在紫外线下产生电信号的材料。简单的检测器使用涂有化学物质的试纸，这些物质遇紫外线会变色。
The UV Index (UVI) is a standard scale used to indicate the intensity of solar UV radiation at ground level. A UVI of 1–2 is low, while a UVI of 11+ is extreme. Many weather forecasts report the UVI to help people plan outdoor activities.
紫外线指数（UVI）是表示地面太阳紫外线辐射强度的标准标度。UVI为1–2表示低，UVI为11以上表示极强。许多天气预报会报告UVI，以帮助人们规划户外活动。
12. Summary and Revision Tips | 总结与复习要点
In this article, we explored ultraviolet radiation using the example of 357 nm. We learned that UV sits between visible light and X-rays, is divided into UVA, UVB, and UVC, and carries enough energy to damage DNA. We also saw how the ozone layer protects us and why sunscreen is important
Published by TutorHao | IGCSE Science Revision Series | aleveler.com
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