Problem
Problem
White light is incident from under water on the water-air interface. If the angle of incidence is slowly increased from zero, the emergent beam coming out into the air will turn from a. white to violet b. white to red c. white to black d. None of theseIntuitive explanation
The key concept here is total internal reflection and the critical angle. When light travels from a denser medium (water) to a less dense one (air), refraction bends the ray away from the normal. As you increase the angle of incidence, the refracted ray bends more and more steeply until it reaches 90° to the normal—this is the critical angle. Beyond that point, no light escapes; instead, all light reflects back into the water. So the emergent beam gradually becomes dimmer and eventually disappears entirely.
Intuitive explanation
The key concept here is total internal reflection and the critical angle. When light travels from a denser medium (water) to a less dense one (air), refraction bends the ray away from the normal. As you increase the angle of incidence, the refracted ray bends more and more steeply until it reaches 90° to the normal—this is the critical angle. Beyond that point, no light escapes; instead, all light reflects back into the water. So the emergent beam gradually becomes dimmer and eventually disappears entirely.