Question: What is the minimum thickness of a soap bubble for which the first order of constructive interference occurs for light of wavelength 600 nm?

Options:

1. 100 nm
2. 200 nm
3. 300 nm
4. 400 nm

Correct Answer: 200 nm

Solution:

For constructive interference in a soap bubble, the minimum thickness t = λ/2 = 600 nm / 2 = 300 nm.