Frequency of sound wave is 600Hz. This wave Incidens perpendicular to open door of width 0.75m. At which angle is the first minima obtained ? (speed of light in air = `330 ms^(-1))`

Options

A. `20.8`
B. `45^(@)`
C. `47.2^(@)`
D. `83.6^(@)`

Answer

C

Explanation

For `m^(th)` order minima `d sin theta_(m)=m lambda`
`0.75 sin theta_(1)= lambda ....(1)`
But `v=lambda f rArr =(v)/(f)`
`0.75 sin theta_(1)=(v)/(f)`
`:. sin theta_(1)=(v)/(fxx0.75)=(330)/(600x0.75)=0.7333`
`:.sintheta_(1)=0.7333`
`:.theta_(1)=47^(@)=10.~~47.2^(@)`