Interference and diffraction are phenomena explained by wave superposition, thus supporting the wave nature of light.
1537
When one of the slits of Young's experiment is covered with a transparent sheet of thickness 4.8 mm, the central fringe shifts to a position originally occupied by the 30th bright fringe. What should be the thickness of the sheet if the central fringe has to shift to the position occupied by 20th bright fringe?
Shift is proportional to thickness, so new thickness = 4.8 × (20/30) = 3.2 mm.
1538
In Young's double-slit experiment the wavelength of light was changed from 7000 Å to 3500 Å. While doubling the separation between the slits which of the following is NOT true for this experiment?
Both bright and dark fringe spacings depend on wavelength and slit separation, so they change; statement D is false.
1539
Coherent light is incident on two fine parallel slits S1 and S2 as shown in Fig. 17. If a dark fringe occurs at P, which of the following gives possible phase differences for the light waves arriving at P from S1 and S2 ?
Dark fringes occur when phase difference is an odd multiple of π, i.e., π, 3π, 5π, ... corresponding to destructive interference.
1540
Monochromatic blue light has been used to obtain the diffraction pattern of a narrow slit on a screen. Keeping the experimental set-up unchanged if blue light is replaced by red monochromatic light, the diffraction pattern will
