Solving Thin Films Interference Problem with Oil and Water | 360nm Thickness

[nabilsaleh]

Homework Statement

A 360 nm thick oil film floats on the surface of the water. The indices of refraction of the oil and the water are 1.50 and 1.33, respectively. The surface of the oil is illuminated from above at normal incidence with white light. The two wavelengths of light in the 400 nm to 800 nm wavelength band that are most strongly reflected, in nm, are closest to:

A) 410 and 700
B) 430 and 720
C) 450 and 740
D) 470 and 760
E) 490 and 780

this is one of questions that came up in the previous exams but i couldn't solve it and i couldn't find the answer online.

Homework Equations

i'm guessing we should use this :

2L=((m+1/2)*lamda)/n

n is the index of refraction
lamda is the wavelength

The Attempt at a Solution

ans is B

 

[member 553083]

) 430 and 720 2*360 nm = ((m+1/2)*lamda)/1.50lamda = 1280 nm m=4 2L=((m+1/2)*lamda)/n 2L=((4+1/2)*1280/1.33)2L=1523.8 L=761.9 so lamda is 761.9 nm and 1260-761.9=428.1 nm so B) 430 and 720 is the closest ans Thanks in advance.