Thin-Film Interference · 薄膜干涉
A soap bubble is colourless — so why the swirling rainbows?
- Soap and water are clear, yet a bubble shimmers with swirling colours.
- A thin film of oil on a wet road does the same.
- The colours come from light reflecting off both surfaces of the thin film and interfering.
- It is interference again — this time from a film only a wavelength or two thick.
肥皂泡是无色的——那旋转的彩虹从哪来?
- 肥皂和水都是透明的,可肥皂泡却闪着旋转的色彩。
- 湿路面上的一层薄油也一样。
- 这些颜色来自光从薄膜的两个表面反射并干涉。
- 又是干涉——这次来自只有一两个波长厚的薄膜。
Two reflections interfere
- When light hits a thin film, part reflects off the top surface and part off the bottom.
- The two reflected waves travel slightly different distances, then overlap and interfere.
- Depending on the film's thickness and the light's wavelength, they add or cancel.
- The result is bright or dark for each colour, giving the shimmering hues.
两次反射相干涉
- 当光打到薄膜上时,一部分从上表面反射,一部分从下表面反射。
- 两道反射波走过略微不同的距离,然后重叠并干涉。
- 依薄膜的厚度和光的波长,它们相加或相消。
- 结果是每种颜色变亮或变暗,给出闪烁的色调。
The colours of a soap bubble come from: · 肥皂泡的颜色来源于：
Reflections off the top and bottom surfaces interfere, producing colours. · 上下表面的反射光发生干涉，产生颜色。
Why the colours change
- The extra path in the film is set by its thickness, so different thicknesses favour different colours.
- As a bubble's wall thins and swirls, the thickness changes and so do the colours.
- One wavelength cancels while another adds, so white light splits into shifting hues.
- Where the film is thinnest (about to pop), it can look black — all colours cancel.
颜色为何变化
- 薄膜内多走的路程由它的厚度决定,所以不同厚度偏爱不同颜色。
- 随着泡壁变薄、旋转,厚度改变,颜色也随之改变。
- 一种波长相消而另一种相加,所以白光分成变幻的色调。
- 薄膜最薄处(即将破裂)可能看起来是黑的——所有颜色都相消。
Which property of the film decides which colours add or cancel? · 薄膜的哪个属性决定了哪些颜色相加或抵消？
The film's thickness sets the extra path, so it decides the interference for each colour. · 薄膜厚度设定了额外路径差，从而决定每种颜色的干涉结果。
Select all · 所有 true statements about thin-film interference. · 选择关于薄膜干涉的所有正确陈述。
Thin-film colours come from two-surface interference set by thickness, and power anti-reflection coatings. No pigments involved. · 薄膜颜色源于由厚度决定的双表面干涉，并能实现减反射功能。不涉及色素。
Useful thin films
- Anti-reflection coatings on camera lenses and glasses use thin films to cancel reflected light.
- The coating is made exactly the right thickness to make reflections interfere destructively.
- That lets more light through the lens and cuts glare.
- The same physics that colours a bubble makes your glasses reflect less.
有用的薄膜
- 相机镜头和眼镜上的增透膜用薄膜来抵消反射光。
- 镀膜厚度做得恰到好处,使反射发生相消干涉。
- 这让更多光穿过镜头并减少眩光。
- 给泡着色的同一物理,让你的眼镜反射更少。
Bright or dark film? · 亮膜还是暗膜？
A thin film looks bright or dark depending on how the reflected waves combine. Sort each case. · 薄膜的亮暗取决于反射波的叠加方式。对每种情况进行排序。
A soap film about to burst can look black because: · 即将破裂的肥皂膜可能看起来是黑色的，因为：
When very thin, the two reflections cancel for all colours, so little light reflects. · 当薄膜极薄时，两束反射光对所有颜色都发生相消干涉，因此几乎没有光反射。
Lens coatings that use thin films to cancel reflected light are called ____-reflection coatings. · 利用薄膜相消反射光来减少反射的镜头涂层称为____反射涂层。
Anti-reflection coatings make reflections interfere destructively. · 减反射涂层使反射光发生相消干涉。
The colours of a soap bubble are not pigments — soap is colourless. They come from interference between light reflected off the two surfaces of the film. As the film's thickness changes, which colours cancel and which add changes too, so the colours swirl.
肥皂泡的颜色不是颜料——肥皂是无色的。它们来自薄膜两个表面反射光之间的干涉。随着薄膜厚度改变,哪些颜色相消、哪些相加也改变,所以颜色旋转。
Soap-bubble colours are caused by pigments in the soap. · 肥皂泡的颜色是由肥皂中的色素引起的。
Soap is colourless; the colours come from thin-film interference. · 肥皂是无色的；颜色来自薄膜干涉。
Why does a soap film sometimes look black just before it bursts?
- The film has thinned to almost nothing, so the path difference is nearly zero — but the top-surface reflection flips by half a wavelength while the bottom one does not, so the two reflections end up out of step and cancel.
- Every visible colour interferes destructively, so little light reflects — it looks dark.
为什么肥皂膜在即将破裂前有时看起来是黑的?
- 薄膜已经薄到几乎为零,所以路径差几乎为零——但上表面的反射翻转半个波长,而下表面的不翻转,所以两次反射最终反相并相消。
- 每一种可见颜色都发生相消干涉,所以几乎没有光反射——看起来是暗的。
Thin-film interference colours soap bubbles and oil slicks: light reflecting off the film's two surfaces overlaps and interferes. The thickness decides which colours add or cancel, so the hues shift as the film changes. The same effect powers anti-reflection coatings on lenses.
薄膜干涉给肥皂泡和油膜着色:从薄膜两个表面反射的光重叠并干涉。厚度决定哪些颜色相加或相消,所以随薄膜变化色调也变。同一效应驱动镜头上的增透膜。