In Young's Double Slit Experiment, we were taught that light behaves as a wave here because the width of the slits are very close to the wavelength of light itself. But why does light behave like a wave only when it interacts with objects that have dimensions close to the wavelength of light? Even in my book no explanation is given as to why this is true. Can someone please explain as to why this is true? I am so confused.
Optics – Why Light Shows Wave-Like Properties Only with Objects Close to Its Wavelength
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Best Answer
It is somewhat misleading to say that light behaves as a wave only when it interacts with objects that have dimensions comparable with its wavelength. It would be closer to reality to say that its wavelike properties are more apparent in such circumstances.
If you want an analogy to help you develop a mental picture of what is happening, imagine a cork and a supertanker floating on a sea that is initially perfectly flat.
If ripples with a wavelength of a few inches travel over the surface of the sea, the cork will ride up and down with them- the motion of the cork will faithfully reflect the wave-like nature of the ripples, but the supertanker will be undisturbed. Being so much longer than the wavelength of the ripples, the supertanker will experience the effects of many ripples averaged out, the effects of their peaks being averaged out by the effects of their troughs.
Conversely, in a gentle swell with a wavelength comparable to length of the supertanker, the ship will seesaw- the bow will sink in a trough while the stern is raised by a peak.