Question

What is the angular fringe width \(\alpha\)?

Options

• \[\alpha=\frac{\lambda D}{d}\]

• \[\alpha=\frac{D}{\beta}=\frac{d}{\lambda}\]

• \[\alpha=\frac{\beta}{d}=\frac{\lambda}{D}\]

• \[\alpha=\frac{\beta}{D}=\frac{\lambda}{d}\]

Answer 1

Angular fringe width is fringe width divided by screen distance, \(\frac{\beta}{D}\). Substituting \(\beta=\frac{\lambda D}{d}\) gives \[\alpha=\frac{\lambda}{d}\].