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

  $\mathrm{d}/\mathrm{\lambda }$

• B

  $\text{2λ/d}$

• C

  ${\mathrm{d}}^2/2\mathrm{\lambda }$

• D

  $2{\mathrm{\lambda }}^2/\mathrm{d}$