Visible light travels in air, which has an index of refraction of 1.0. It is incident on plastic which is covered by a coating (such that light hits the coating before the plastic). The coating has an index of refraction of 1.6 and is 0.50 microns thick. The ray reflected off the air-coating interface and the ray reflected off the coating-plastic interface experience interference. What frequencies could the light be

  λ = 0.64 10⁻⁶ m = 640 nm

Explanation:

The two reflected rays experience constructive interference, if we can see them, so we can one condition for interference, but let's see two phenomena that occur

* A ray when it is reflected by a surface of major spare part index has a phase change of 180º, these passes at the air-plastic interface

* A ray when passing a material with a refractive index changes its wavelength

       λ= λ₀ / n

taking into account these facts the condition in constructive interference is

             2 n t = (m + ½) λ

             λ= 2 n t / (m + ½)

if we suppose that we have the first inference m = 0

            λ = 2 1.6 0.5 10⁻⁶ (0 + ½)

            λ = 3.2 10⁻⁶ m

this wavelength is in the infrared

suppose an interference of m = 1

          λ = 1.6 10⁻⁶ / (1 + 1/2)

          λ = 1.06 10-6 m

m = 2

         λ = 1.6 10⁻⁶ / (2 + 1.5)

         λ = 0.64 10⁻⁶ m

this wavelength corresponds to the visible range (640 nm) orange

air exerts forces on falling objects near earth’s surface.

explanation:

the term 'free falls' refer to object that are falling towards the earth, in a situation in which gravity is the only force acting on the object.

for an object in free fall, the acceleration is constant (g, the gravitational acceleration), and so the velocity of the object constantly increases.

for objects near earth's surface, there is always another force acting on the object: the resistance due to the air. this force is opposed to the direction of fall of the object, and it is proportional to the velocity of the object, so as the object falls down, this force increases up to a point when it balances the force of gravity, and the object continues its motion at constant velocity (called terminal velocity). since in this case gravity is not the only force acting on the object, we are not in a situation of free fall.