# Why does wavelength affect diffraction?

This question came up in the biology section

Q1: The longer the wavelength of a wave, the more easily it bend around an obstacle. I do understand the mathematics, but is there any intuition for it?

Q2A: Is this an acceptable explanation, or is it misleading?

"If light were fundamentally a ray, then it makes sense that it would travel in straight lines. But if you think light is a wave, then it makes sense that it would not travel in straight lines. After all, if you put an obstacle in the path of waves in the sea, the waves can go around the obstacle. The bigger the obstacle, the less the waves can go around it. On the other hand, the bigger the wavelength, the smaller the obstacle is relative to the wave, so this gives some intuition as to why wavelength affects bending around an obstacle."

Q2B: If the above is acceptable, is it acceptable for all wave diffraction, or only for some, eg. ok for water waves or air, but not for electromagnetic waves?

Drakkith
Staff Emeritus
Q2A: Is this an acceptable explanation, or is it misleading?

"If light were fundamentally a ray, then it makes sense that it would travel in straight lines. But if you think light is a wave, then it makes sense that it would not travel in straight lines. After all, if you put an obstacle in the path of waves in the sea, the waves can go around the obstacle. The bigger the obstacle, the less the waves can go around it. On the other hand, the bigger the wavelength, the smaller the obstacle is relative to the wave, so this gives some intuition as to why wavelength affects bending around an obstacle."

Sure, that's acceptable. Light is just a really short wavelength EM wave, so if you think about long-wavelength radio waves, they do indeed diffract around everyday objects.

Q2B: If the above is acceptable, is it acceptable for all wave diffraction, or only for some, eg. ok for water waves or air, but not for electromagnetic waves?

It should apply to all types of waves.