Answer:
a) 2232nm
b) 2511nm
Explanation:
a) To find the path difference Δl you use the following formula:
[tex]\Delta l=m\lambda[/tex]
m: order of a bright fringe
λ: wavelength of light = 558nm
for m=4:
[tex]\Delta l=(4)(558nm)=2232nm[/tex]
b) The path difference for the case of destructive interference you have:
[tex]\Delta l=(m+\frac{1}{2})\lambda[/tex]
m: order of a dark fringe
for m=4:
[tex]\Delta l=(4+\frac{1}{2})(558nm)=2511nm[/tex]