At exactly the critical angle:
a) all light reflects back into the n1 medium
b) all light reflects back into the n2 medium
c) part of the light reflects back into the n1 medium, the remainder travels along the boundary between the two mediums
d) part of the light reflects back into the n2 medium, the remainder travels along the boundary between the two mediums
The critical angle is defined as the angle of incidence at which light is refracted along the boundary between two transparent media. To determine what happens at the critical angle, we need to consider the different possibilities:
a) At the critical angle, if the angle of incidence is equal to the critical angle, all the light reflects back into the medium with a lower refractive index (n1). This is known as total internal reflection, which occurs when light tries to pass from a medium with a higher refractive index (n2) to a medium with a lower refractive index, but the angle of incidence is too large.
b) If the angle of incidence is equal to the critical angle, none of the light reflects back into the medium with a higher refractive index (n2). Instead, all the light is refracted along the boundary between the two media. This is not observed at the critical angle.
c) At any angle of incidence less than the critical angle, part of the light reflects back into the medium with a lower refractive index (n1), while the remainder continues to travel along the boundary between the two media. Total internal reflection will not occur at any angle less than the critical angle.
d) At any angle of incidence less than the critical angle, part of the light reflects back into the medium with a higher refractive index (n2), while the remainder continues to travel along the boundary between the two media. Total internal reflection will not occur at any angle less than the critical angle.
Therefore, the correct answer is:
d) Part of the light reflects back into the n2 medium, and the remainder travels along the boundary between the two mediums.