Electromagnetic Waves · 电磁波
| English | 中文 | Pinyin · 拼音 |
|---|---|---|
| electromagnetic wave/ɪˌlektrəʊməɡˈnetɪk weɪv/ | 电磁波 | diàn cí bō |
Radio, heat, light, X-rays — all the same kind of wave
- Your radio, your microwave, sunlight and a hospital X-ray seem worlds apart.
- Yet they are all the same thing: electromagnetic waves, differing only in wavelength.
- An electromagnetic wave 电磁波 is a self-sustaining ripple of electric and magnetic fields.
- Lined up by wavelength, they form the electromagnetic spectrum.
无线电、热、光、X 射线——全是同一种波
- 你的收音机、微波炉、阳光和医院的 X 射线,看起来天差地别。
- 可它们全是同一种东西:电磁波,只在波长上不同。
- 电磁波是电场和磁场自我维持的一道涟漪。
- 按波长排列,它们构成电磁波谱。
What an EM wave is
- An EM wave is a wave of oscillating electric and magnetic fields, at right angles to each other.
- It needs no medium — it travels through empty space (that's how sunlight reaches us).
- All EM waves travel at the speed of light $c$ in a vacuum ($\approx 3\times10^8\ \tfrac{\text{m}}{\text{s}}$).
- They are transverse waves, which is why light can be polarised.
什么是电磁波
- 电磁波是振荡的电场和磁场的波,两者相互垂直。
- 它不需要介质——它穿过真空传播(阳光就是这样到达我们的)。
- 所有电磁波在真空中都以光速 $c$ 传播($\approx 3\times10^8\ \tfrac{\text{m}}{\text{s}}$)。
- 它们是横波,这就是光能被偏振的原因。
In a vacuum, radio waves and X-rays travel at: · 在真空中，无线电波和X射线的速度：
All EM waves travel at the speed of light $c$ in a vacuum. · 所有电磁波在真空中的速度均为 $c$。
Electromagnetic waves can travel through empty space with no medium. · 电磁波可在无介质的真空中传播。
EM waves need no medium — that's how sunlight crosses space to Earth. · 电磁波无需介质——这正是阳光能穿越太空到达地球的原因。
EM waves are ____ waves, which is why light can be polarised. · 电磁波是 ____ 波，这也是光可以被偏振的原因。
EM waves are transverse (fields perpendicular to travel), so they can be polarised. · 电磁波是横波（场垂直于传播方向），因此可以被偏振。
The spectrum
- In order of increasing frequency (decreasing wavelength): radio, microwave, infrared, visible, ultraviolet, X-ray, gamma.
- Visible light is just a thin band our eyes happen to detect — red (long $\lambda$) to violet (short $\lambda$).
- Higher-frequency waves (UV, X-ray, gamma) carry more energy per photon and can be harmful.
- Lower-frequency waves (radio, micro) are gentler and carry information and heat.
波谱
- 按频率递增(波长递减)的顺序:无线电、微波、红外、可见、紫外、X 射线、伽马。
- 可见光只是我们眼睛恰好能探测的一薄条——从红(长 $\lambda$)到紫(短 $\lambda$)。
- 更高频率的波(紫外、X 射线、伽马)每个光子携带更多能量,可能有害。
- 更低频率的波(无线电、微波)更温和,携带信息和热。
Explore the spectrum · 探索光谱
Slide across the spectrum from radio to gamma and see the wavelength and uses change. · 从无线电波滑动至伽马射线，观察波长和用途的变化。
Which has the highest frequency? · 哪一种具有最高频率？
Gamma rays are at the high-frequency (short-wavelength) end of the spectrum. · 伽马射线位于频谱的高频（短波长）端。
Higher-frequency EM waves (like X-rays) carry more energy per photon than radio waves. · 高频电磁波（如X射线）每个光子携带的能量高于无线电波。
Photon energy rises with frequency, so X-rays carry more per photon than radio. · 光子能量随频率升高而增加，因此X射线每个光子携带的能量高于无线电波。
Select all · 所有 true statements about electromagnetic waves. · 选择关于电磁波的所有正确陈述。
All EM waves are transverse, need no medium, and travel at $c$. Radio is not slower than light. · 所有电磁波均为横波，无需介质，并以 $c$ 传播。无线电波并不比光速慢。
Everyday uses
- Radio & micro — communications, cooking, radar.
- Infrared — heat, remote controls, night vision.
- Visible & UV — sight, sunburn, sterilisation.
- X-ray & gamma — medical imaging, cancer treatment, sterilising equipment.
日常用途
- 无线电和微波——通信、烹饪、雷达。
- 红外——热、遥控器、夜视。
- 可见和紫外——视觉、晒伤、消毒。
- X 射线和伽马——医学成像、癌症治疗、器械灭菌。
All EM waves travel at the same speed $c$ in a vacuum — radio is not slower than X-rays. What differs is their wavelength and frequency (and so their energy), not their speed. Since $c = f\lambda$ is fixed, higher frequency always means shorter wavelength.
所有电磁波在真空中都以相同的速率 $c$ 传播——无线电不比 X 射线慢。不同的是它们的波长和频率(以及能量),而非速率。因为 $c = f\lambda$ 固定,更高的频率总意味着更短的波长。
A radio wave and a light wave both travel through a vacuum. Which is faster?
- Neither — both travel at $c \approx 3\times10^8\ \tfrac{\text{m}}{\text{s}}$.
- They differ only in wavelength: the radio wave's is far longer than the light wave's.
一道无线电波和一道光波都穿过真空。哪个更快?
- 都不——两者都以 $c \approx 3\times10^8\ \tfrac{\text{m}}{\text{s}}$ 传播。
- 它们只在波长上不同:无线电波的波长比光波的长得多。
Electromagnetic waves are transverse ripples of electric and magnetic fields that need no medium and all travel at the speed of light $c$ in a vacuum. The spectrum runs radio → gamma by increasing frequency (decreasing wavelength); higher frequency means more energy per photon.
电磁波是电场和磁场的横向涟漪,不需要介质,在真空中全都以光速 $c$ 传播。波谱按频率递增(波长递减)从无线电 → 伽马;频率越高,每个光子的能量越大。