A Level Physics Practice Exam

What condition is necessary for total internal reflection to occur?

1. The angle of incidence is less than the critical angle

2. The refractive index of the second medium is greater than the first

3. The angle of incidence is greater than the critical angle

4. The light must be polarized

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

Total internal reflection occurs under specific conditions when light travels from a medium with a higher refractive index to one with a lower refractive index. For this phenomenon to take place, the angle of incidence must exceed the critical angle, which is the minimum angle at which light is completely reflected within the original medium. When the angle of incidence is greater than the critical angle, the refracted light attempts to pass into the second medium at an angle greater than 90 degrees. Instead of refracting out of the medium, all of the light is reflected back into the first medium. This principle is fundamental in optical devices such as fiber optics, where light signals are transmitted efficiently through total internal reflection. Understanding this condition is important in applications that rely on light behavior at boundaries between different media, such as prisms and optical fibers. The other choices do not describe the correct scenario for total internal reflection to occur.