The radius $r$ of the $n^{th}$ half-period zone is proportional to:

Light of wavelength $\lambda$ is incident on a slit of width $d$. The resulting diffraction pattern is observed on a screen at a distance $D$. The linear width of the principal maximum is then equal to the width of the slit if $D$ equals

$A$ narrow slit of width $2 \, mm$ is illuminated by monochromatic light of wavelength $500 \, nm$. The distance between the first minima on either side on a screen at a distance of $1 \, m$ is ........ $mm$.

$A$ microwave of wavelength $2.0 \ cm$ falls normally on a slit of width $4.0 \ cm$. The angular spread of the central maxima of the diffraction pattern obtained on a screen $1.5 \ m$ away from the slit,will be: (in $^{\circ}$)

The phenomenon that explains why light waves do not travel in a straight line is known as .......

In a single-slit diffraction experiment,the first minimum for a wavelength $\lambda_1 = 660 \ nm$ coincides with the first maximum for a wavelength $\lambda_2$. Find the value of $\lambda_2$ in $nm$.