Question

A teacher stands well back from an outside doorway 0.88 m wide, and blows a whistle of frequency 780 Hz. Ignoring reflections, estimate at what angle(s) it is not possible to hear the whistle clearly on the playground outside the doorway.

Answer 1

the wavelength is to be 56.67 cm and I know that i should be applying the double slit equation for destructive interference.