A Level Physics Practice Exam 2026 – The All-in-One Guide to Mastering Your Physics Exam!

The critical angle is the angle of incidence at which light is refracted at an angle of 90 degrees when moving from a medium of higher refractive index to a medium of lower refractive index. This phenomenon can be described using Snell's Law, which relates the angles of incidence and refraction to the refractive indices of the two media involved.

The correct relationship for the critical angle is based on Snell's Law, which states that n1 * sin(angle of incidence) = n2 * sin(angle of refraction). For the critical angle, the angle of refraction is 90 degrees. Hence, sin(90 degrees) is equal to 1, simplifying the equation to n1 * sin(critical angle) = n2 * 1.

This is consistent with the definition that, at the critical angle, light no longer exits into the second medium but is instead totally internally reflected. Therefore, the correct expression captures the essence of the critical angle in relation to the refractive indices of the two media.

The equations that involve sin(angle of incidence) on both sides or incorrectly relate the indices without adherence to the nature of the critical angle do not accurately represent the condition necessary for total internal reflection and do not align with the established