Answer:
[tex] 611.8[/tex] nm
Explanation:
[tex]n_{oil}[/tex] = Index of refraction of soap bubble = 1.33
[tex]t[/tex] = thickness of the soap bubble = 115 nm = 115 x 10⁻⁹ m
[tex]\lambda[/tex] = wavelength of light = ?
[tex]m[/tex] = order = 0
For reflection , the necessary condition is
[tex]2 n_{oil} t = (m + 0.5) \lambda[/tex]
[tex]2 (1.33)(115\times 10^{-9})= (0 + 0.5) \lambda[/tex]
[tex]\lambda = 6.118\times 10^{-7}[/tex]
[tex]\lambda = 611.8[/tex] nm