Under what condition does total internal reflection occur?

Total internal reflection occurs under specific conditions involving the refractive indices of the two media and the angle of incidence. The correct choice states that total internal reflection happens when the refractive index of the first medium (n1) is greater than that of the second medium (n2) and the angle of incidence exceeds the critical angle.

The critical angle is the minimum angle of incidence at which light can pass through the boundary and refract into the second medium. When light attempts to travel from a denser medium (where light is slower) to a less dense medium (where light travels faster) at an angle greater than the critical angle, all the light is reflected back into the denser medium instead of refracting into the less dense one. This phenomenon is crucial in applications such as optical fibers and prism design, where total internal reflection is harnessed to direct light effectively.

The other conditions provided do not fulfill the criteria for total internal reflection. For example, light moving from a denser medium to a less dense medium but at an angle less than the critical angle will refract into the second medium rather than being reflected. Light hitting the boundary perpendicularly would not satisfy the conditions for total internal reflection either, as it would not reach the critical