X-ray Diffraction by Ribs · CAP 2008 #Q8
Physics · optics
Problem
When you receive a chest x-ray at the hospital, the x-rays pass through a set of parallel ribs in your chest. Do your ribs act as a diffraction grating for the X-rays? (a) Yes. They produce diffracted beams that can be observed separately. (b) Not to a measurable extent. The ribs are too far apart. (c) Essentially not. The ribs are too close together. (d) Essentially not. The ribs are too few in number. (e) Absolutely not. X-rays cannot diffract.Intuitive explanation
Diffraction gratings work when the spacing between slits or obstacles is comparable to the wavelength of the wave passing through them. X-rays have extremely short wavelengths (picometers), while human ribs are spaced centimeters apart—vastly larger. When the grating spacing is much bigger than the wavelength, diffraction effects become negligible and the waves essentially travel straight through. The key is comparing length scales: only when obstacle spacing and wavelength are similar do you get observable diffraction patterns.
Intuitive explanation
Diffraction gratings work when the spacing between slits or obstacles is comparable to the wavelength of the wave passing through them. X-rays have extremely short wavelengths (picometers), while human ribs are spaced centimeters apart—vastly larger. When the grating spacing is much bigger than the wavelength, diffraction effects become negligible and the waves essentially travel straight through. The key is comparing length scales: only when obstacle spacing and wavelength are similar do you get observable diffraction patterns.