A two-slit apparatus is covered with a red (670 nm) filter. When white light is shone on the filter, on the screen beyond the two-slit apparatus, there are nine interference maxima within the 4.50 cm-wide central diffraction maximum. When a blue (450 nm) filter replaces the red, how many interference maxima will there be in the central diffraction maximum be?
Physics · Wave Optics
JEE Mains

Question

A two-slit apparatus is covered with a red (670 nm) filter. When white light is shone on the filter, on the screen beyond the two-slit apparatus, there are nine interference maxima within the 4.50 cm-wide central diffraction maximum. When a blue (450 nm) filter replaces the red, how many interference maxima will there be in the central diffraction maximum be?

Physics · Wave Optics

G1 Physics · Accepted Answer

The number of interference maxima inside the central diffraction envelope depends on d/a, because both the interference spacing and diffraction-envelope width scale with λ. Changing from 670 nm to 450 nm leaves this count unchanged. Therefore the count remains 9.