Answer:
2.72 m
Explanation:
wavelength of sound λ = velocity / frequency
= 340 / 1200
= .2833 m
Distance of point of first constructive interference
= λ D / d ( D is distance of the screen and d is distance between source of sound.
Here D = 12.5 m
d = 1.3 m
λ D / d= ( .2833 x 12.5) / 1.3
= 2.72 m
Distance of point of first constructive interference = 2.72 m