Sound from Dr. Who\'s sonic screwdriver leaves a room through a tall doorway wit

Question

Sound from Dr. Who's sonic screwdriver leaves a room through a tall doorway with a width of 1.19 m . The sound has a frequency of 1250 Hz and the speed of sound in air is 344 m/s . At what minimum angle relative to the centerline perpendicular to the doorway would a Dalek outside the room hear no sound, due to wave diffraction? Assume that Dr. Who and the Dalek are both far enough from the doorway for Fraunhofer diffraction to apply. You can ignore effects of reflections. Express your answer in radians.

Explanation / Answer

For first minimum,

dsin =

=> = sin = /d = c/fd = 344 / (1250 * 1.19) = 0.23 rad

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