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To me, as a macroscopic observer of light, it appears that light moves in straight lines. If I shine a light at object A and object B moves between me and object A, the light hits, i.e. gets blocked by object B and no longer hits object A.

However, since light is a transverse wave, doesn't that mean it is oscillating back and forth in space in a dimension perpendicular to its direction of travel? If so, then perhaps it only appears to move in straight lines because of low amplitude or high frequency?

Thus, say there was a radio wave with a wavelength of 1 meter. Could this radio wave then dodge around object B and still hit object A, assuming object B is smaller than 1 meter, say a basketball?

anna v
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Flurrywinde
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2 Answers2

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Thus, say there was a radio wave with a wavelength of 1 meter. Could this radio wave then dodge around object B and still hit object A, assuming object B is smaller than 1 meter, say a basketball?

Waves of large wave lengths can indeed 'wash around' an object that is sufficiently smaller than the wave lengths, a phenomenon called diffraction.

Have a look at the animation embedded in this link and play around with object size to see the effect. For large wavelength to object size ratios the waves down stream from the object are practically undisturbed. It's as if the wave 'doesn't see' the object.

We exploit the inverse effect in electron microscopy to see very small objects, much smaller than the wavelengths of visible light. Electron waves allow to achieve much smaller wavelengths and allows to see much smaller objects.

The importance of Long Wave radio waves for similar reasons is explained in this link.

Whether the waves are of transversal or longitudinal character is irrelevant here: sound waves (longitudinal) show diffraction too.

Gert
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Aragos or Poisson spot

During the 19th century scientists were still undecided if light is a wave phenomenon or consisting of particles. Poisson thought he refuted the wave theory by predicting correctly that a bright point should appear in the middle of a shadow if the light and the object are prepared in a specific way. Arago actually tried this and saw the "impossible" spot:

Arago spot

Thorsten S.
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