Red light differs from blue light in its

Light from a point source falls on a small area placed perpendicular to the incident light. If the area is rotated about the incident light by an angle of $60^o$,by what fraction will the illuminance change?

Write the difference between the interference pattern and diffraction pattern.

$\lambda_{1}$ and $\lambda_{2}$ are used to illuminate the slits. $\beta_{1}$ and $\beta_{2}$ are the corresponding fringe widths. The wavelength $\lambda_{1}$ can produce photoelectric effect when incident on a metal. But the wavelength $\lambda_{2}$ cannot produce photoelectric effect. The correct relation between $\beta_{1}$ and $\beta_{2}$ is

$A$ laser beam can be focused on an area equal to the square of its wavelength. $A$ $He-Ne$ laser radiates energy at the rate of $1 \, mW$ and its wavelength is $632.8 \, nm$. The intensity of the focused beam will be:

Which colour of the light has the longest wavelength?