Question

a parallel beam of monochromatic light is incident on a slit of width 3 cm. the light passing though the slit falls on a screen 4 m away. as the slit width is decreased,

the width of the pattern on the screen at first decreases but then increases.

the width of the pattern on the screen remains the same.

the width of the pattern on the screen continuously decreases.

the width of the pattern on the screen increases and then decreases.

the width of the pattern on the screen continuously increases.

Explanation:

This problem relates to the diffraction of light, a concept in Physics (subfield of Natural Science). The formula for the width of the central maximum in single - slit diffraction is $\Delta y=\frac{2\lambda D}{a}$, where $\lambda$ is the wavelength of light, $D$ is the distance between the slit and the screen, and $a$ is the width of the slit. When the slit width $a$ is decreased (while $\lambda$ and $D$ remain constant), from the formula, we can see that the width of the central maximum (and thus the width of the diffraction pattern) is inversely proportional to the slit width. So as $a$ decreases, $\Delta y$ (the width of the pattern) continuously increases.

Answer:

the width of the pattern on the screen continuously increases.