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:

$A$ diffraction pattern is obtained by using a beam of red light. What will happen if the red light is replaced by blue light?

$A$ parallel beam of fast-moving electrons is incident normally on a narrow slit. $A$ fluorescent screen is placed at a large distance from the slit. If the speed of the electrons is increased,which of the following statements is correct?

The phenomenon of diffraction was discovered by ...... .

$A$ slit of width $d$ is illuminated by light of wavelength $\lambda$. The angular width of the central maximum is:

$A$ circular disc is placed in front of a narrow source. When the point of observation is at a distance of $1 \, m$ from the disc,the disc covers the first $HPZ$ (Half Period Zone). The intensity at this point is $I_0$. The intensity at a point at a distance of $25 \, cm$ from the disc will be: