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
To determine what happens at the critical angle, we need to understand the concept of total internal reflection. Total internal reflection occurs when light travels from a medium with a higher refractive index to a medium with a lower refractive index, and the angle of incidence is greater than or equal to the critical angle.
The critical angle (θc) can be calculated using the formula:
sin θc = n2 / n1
Where:
- θc is the critical angle,
- n1 is the refractive index of the first medium (incident medium),
- n2 is the refractive index of the second medium (transmitting medium).
Now, let's consider the given options:
a) all light reflects back into the n1 medium:
This option is incorrect because at the critical angle, the light undergoes total internal reflection and stays entirely within the n1 medium, not returning to it.
b) all light reflects back into the n2 medium:
This option is also incorrect because at the critical angle, the light undergoes total internal reflection and does not enter the n2 medium.
c) part of the light reflects back into the n1 medium, the remainder travels along the boundary between the two mediums:
This option is correct. At the critical angle, some of the light reflects back into the n1 medium, while the rest continues to travel 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:
This option is incorrect. At the critical angle, all of the incident light is reflected back into the n1 medium and none of it enters the n2 medium.
Therefore, the correct answer is option c) part of the light reflects back into the n1 medium, the remainder travels along the boundary between the two mediums.