Answer:
a) that laser 1 has the first interference closer to the central maximum
c) Δy = 0.64 m
Explanation:
The interference phenomenon is described by the expression
d sin θ = m λ
Where d is the separation of the slits, λ the wavelength and m an integer that indicates the order of interference
For the separation of the lines we use trigonometry
tan θ = sin θ / cos θ = y / x
In interference experiments the angle is very small
tan θ = sin θ = y / x
d y / x = m λ
a) and b) We apply the equation to the first laser
λ = d / 20
d y / x = m d / 20
y = m x / 20
y = 1 4.80 / 20
y = 0.24 m
The second laser
λ = d / 15
d y / x = m d / 15
y = m x / 15
y = 0.32 m
We can see that laser 1 has the first interference closer to the central maximum
c) laser 1
They ask us for the second maximum m = 2
y₂ = 2 4.8 / 20
y₂ = 0.48 m
For laser 2 they ask us for the third minimum m = 3
In this case to have a minimum we must add half wavelength
y₃ = (m + ½) x / 15
m = 3
y₃ = (3 + ½) 4.8 / 15
y₃ = 1.12 m
Δy = 1.12 - 0.48
Δy = 0.64 m