A Level Physics Practice Exam

What condition must be met for total internal reflection to occur?

1. The angle of incidence must be less than the critical angle

2. The refractive index of the second medium must be greater

3. The angle of incidence must be greater than the critical angle

4. The refractive index of both media must be equal

The correct answer is: The angle of incidence must be greater than the critical angle

Total internal reflection occurs when light attempts to move from a medium with a higher refractive index to one with a lower refractive index, and it does so at an angle greater than the critical angle. The critical angle is defined as the specific angle of incidence where the refracted light would travel along the boundary between the two media. If the angle of incidence is greater than this critical angle, the light cannot refract into the second medium; instead, it reflects back completely into the first medium. This phenomenon is exploited in various applications, such as fiber optics, where efficient light transmission is achieved. In contrast, if the angle of incidence is less than the critical angle, the light will refract rather than reflect, meaning total internal reflection does not occur. Additionally, if the refractive index of the second medium is greater than that of the first, refraction would happen regardless of the angle of incidence. Lastly, when the refractive indices of both media are equal, light would not reflect at all but rather pass straight through the boundary. Therefore, the condition for total internal reflection to occur is that the angle of incidence must indeed be greater than the critical angle.