The principle of reversibility states that light will follow exactly the same path – Free 4B
Principle of Reversibility of Light
Question:
The principle of reversibility states that light will follow exactly the same path if its direction of travel is reversed. This works for reflection. For example, in (a) going left to right, the angle of incidence equals the angle of reflection. If you reverse the direction going right to left, such as in (b), the angle of incidence still equals the angle of reflection. Reversing the direction, the path is still the same. Does the principle of reversibility work for refraction?
Answer:
The principle of reversibility of light states that if a light ray travels from point A to point B along a particular path, then reversing the direction will cause the ray to retrace the same path from B to A.
Application in Reflection:
Consider a light ray striking a flat mirror:
- According to the law of reflection, the angle of incidence equals the angle of reflection.
- In the forward direction, the ray goes from left to right, hits the mirror, and reflects at the same angle.
- If you reverse the direction (right to left), the light approaches from the opposite side but still follows the same angle at the same point on the mirror.
Application in Refraction:
The principle of reversibility can also apply to refraction under certain ideal conditions:
- The medium must be linear and time-invariant.
- There should be no energy absorption or non-linear effects.
- If these conditions are met, then when a light ray enters a new medium (say from air to water) and bends, it will follow the exact reverse path if it exits from water back into air at the same angles.