Final answer:
The reflection coefficient is calculated using the formula: a = (n2 - n1) / (n2 + n1), where n1 is the refractive index of the first medium and n2 is the refractive index of the second medium.
Step-by-step explanation:
When a light wave is incident normally to the interface between two media, the reflection coefficient is given by the formula (Z₂-Z₁)², where Z₁ is the impedance of the first medium and Z₂ is the impedance of the second medium.
The reflection coefficient, also known as the intensity reflection coefficient a, is a dimensionless number that represents the ratio of the intensity of the reflected wave to the intensity of the incident (transmitted) wave.
For normal incidence, if we consider the case of light, impedance can be related to the index of refraction (n) of the medium, substituting Z with n in the formula, the reflection coefficient becomes ((n₂-n₁)/(n₂+n₁))².