Problem

A certain region of a soap bubble reflects red light of vacuum wavelength

\lambda = 650 \text{ nm}

. What is the minimum thickness that this region of the soap bubble could have? Take the index of reflection of the soap film to be 1.41. (1)

1.2 \times 10^{-7} \text{ m}

(2)

650 \times 10^{-9} \text{ m}

(3)

120 \times 10^7 \text{ m}

(4)

650 \times 10^5 \text{ m}