In a single slit experiment, a diffraction pattern is obtained on the screen for yellow light. What will be the effect on the diffraction pattern, if yellow light is replaced by X-rays?
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → diffraction pattern will not be observed
Diffraction is noticeable only when the width of the slit is comparable to the wavelength. The angular spread of the central maximum is about \( \lambda/a \) on each side.
\( \lambda_{\text{yellow}} \approx 6\times10^{-7}\,\mathrm{m} \)
\( \lambda_{\text{X-ray}} \approx 10^{-10}\,\mathrm{m} \)
X-rays have a wavelength thousands of times smaller, so their spread \( \lambda/a \) (about \( 10^{-6} \) rad) is far too small to be seen: they pass straight through the slit. No diffraction pattern is observed.
Option (1) diffraction pattern will not be observed — Correct. The wavelength of X-rays is far smaller than the slit width, so the bending is negligible and no pattern can be seen.
Option (2) number of fringes will decrease — Incorrect. There is no visible pattern at all, so there are no fringes to count.
Option (3) number of fringes will increase — Incorrect. Same reason: no fringes are seen with X-rays.
Option (4) central maximum will become narrower — Incorrect. \( 2\lambda/a \) shrinks so much that no separate central maximum is seen.