Question Detail
Question
A ray of light travels through transparent plastic to air. The ray of light enters the air travelling parallel to the surface of the plastic. The refractive index of the plastic is 1.25. What is angle θ?
Correct Answer
Option D is the correct answer.
Detailed Explanation
The problem describes a situation where a ray of light is traveling from a denser medium (plastic) to a less dense medium (air). The ray enters the air traveling parallel to the surface of the plastic, which means the angle of refraction in the air is 90°. In this specific case, the angle of incidence in the plastic, θ, is the critical angle (θc).Using Snell's Law for the critical angle:nplastic * sin(θc) = nair * sin(90°)Given:nplastic = 1.25nair = 1 (refractive index of air is approximately 1)sin(90°) = 1Substitute the values into the equation:1.25 * sin(θ) = 1 * 1sin(θ) = 1 / 1.25sin(θ) = 0.8To find θ, take the inverse sine:θ = arcsin(0.8)θ ≈ 53.13°Rounding to the nearest degree, θ ≈ 53°.
Hint
When a ray travels from a denser to a less dense medium and emerges parallel to the surface, the angle of incidence is the critical angle. Use Snell's Law.