Question

What is the minimum thickness of a soap bubble needed for constructive interference in reflected light if the light incident on film is of wavelength 900 nm. Refractive index of film is 1.5

• A. 100 nm
• B. 150 nm
• C. 200 nm
• D. 250 nm

Answer 1

Answer: (B)

150 nm

Answer 2

2 mt cos r = (2n_ 1) $\frac{\lambda}{2}$

Ž t = $\frac{(2n - 1) \times 900}{4 \times 1.5 \times 1}$

\ t = 150 nm (n = 1)