The diffraction pattern of light of wavelength $400 \ nm$ diffracting from a slit of width $0.2 \ mm$ is focused on the focal plane of a convex lens of focal length $100 \ cm$. The width of the $1^{\text{st}}$ secondary maxima will be:

The diffraction fringes obtained from a single slit are.....

$A$ parallel beam of monochromatic light is incident on a narrow rectangular slit of width $1\,mm$. When the diffraction pattern is seen on a screen placed at a distance of $2\,m$, the width of the principal maxima is found to be $2.5\,mm$. The wavelength of light is $.............\mathring{A}$.

If a classroom door is open just a small amount, we can hear sounds coming from the room but we can't see what is going on inside the room because

The diffraction effect can be observed in

In a single-slit diffraction experiment, the slit is illuminated by light of two wavelengths $\lambda_1$ and $\lambda_2$. It is observed that the $2^{nd}$ order diffraction minimum for $\lambda_1$ coincides with the $3^{rd}$ diffraction minimum for $\lambda_2$. Then: