Which electromagnetic wave has wavelengths ranging from the size of a printed period

the bubble appears DARK

Explanation:

This problem shows the interference by reflection of light on the surface, let's take it into account;

* There is a phase change of 180º on the surface when it stops from a lower medium to a higher index

* Within the film the wavelength changes due to the fraction index

if we plug this into the expression for constructive interference we have

       2tn = (m + ½) λ₀

for destructive interference it is

       2tn = m λ₀

apply these expressions to our case

indicate that the incident wavelength is red λ₀ = 700 nm

Let's find the minimum thickness that the film must have to have a constructive interference

the refractive index of soap is n = 1.4

from the constructive interference equation

            t = (0+ ½) 700 10⁻⁹ / 2 1.4

            t = 1.25 10⁻⁷ m

just before the soap bubble explodes the thickness (t) of the film less than the calculated value there is no possibility of constructive interference, therefore the bubble appears DARK