Light - Internal Reflection

Question 1

reflection

Answer 1

• When a ray in a higher n (denser) medium, like glass, exits into a lower n (less dense) medium, like air, the ray will bend away from the normal, to a larger angle. As you increase the incident angle, the refracted angle gets larger and larger. However, because the refracted angle is bigger than the incident, it will eventually reach 90 degrees before the incident angle does. A ray that refracts 90 degrees from the normal will just skim the surface between the two media.
• If the angle goes greater than 90 degrees, then the refracted doesn’t enter the second medium at all. Instead, it reflects back into the original medium; the surface acts as a mirror for the ray. This is called “Internal Reflection.” It happens any time a ray in a denser medium hits a surface at an angle greater than the critical angle. If that is the case, the ray reflects at the same angle it hit at
• Note this ONLY happens when a ray is in a denser high-n region and is trying to enter a less dense low-n region. If that is the case, you need to find the critical angle and see if the incident angle is greater than it. If so, it reflects; if not, it refracts into the second medium at a greater angle.