Answer:
y’= 2 cm
Step-by-step explanation:
In the system with more than two slits we can consider them a network and diffraction, which is described by the expression
d sin θ = m λ
Where d is the separation between the slits, λ the wavelength and m an integer that is the order of diffraction.
Let's use trigonometry for line separation
tan θ = y / L
Where L is the distance to the observation screen, in diffraction and measured angle experiments it is small
tan θ = sin θ / cos θ = sin θ
We replace
d y / L = m λ
This is the equation for constructive interference, it indicates that y = 8 cm for m = 2
d 8 / L = 2 λ
d / Lλ = 2/8
For the case destructive interference we must increase the length is wave is λ/2, the equation remains
d y’/ L = (m + ½) λ
In the case of adjacent strips m = 0
d y’/ L = (0+ 1/2) λ
d / Lλ = 1 / 2y’
Let's match the two diffraction equations
¼ = 1 / 2y’
2y’= 4
y’= 2 cm