Normal incidence of light on a denser medium

[akhila_k]

When light, traveling through a rarer medium, gets reflected off at an interface with a medium of higher refractive index, it suffers a phase shift of half-wavelength. Now if it was normal incidence, the phase-shifted light would retrace its path. Does that mean the wave would cancel out?

 

[sophiecentaur]

When light, traveling through a rarer medium, gets reflected off at an interface with a medium of higher refractive index, it suffers a phase shift of half-wavelength. Now if it was normal incidence, the phase-shifted light would retrace its path. Does that mean the wave would cancel out?

The boundary conditions at the interface insist that the waves cancel out. As you look further away from the interface you pass through regions where the waves augment and cancel - i.e. a standing wave pattern. Power flows to the right and to the left. You don't actually lose any Power.

 

[akhila_k]

The boundary conditions at the interface insist that the waves cancel out. As you look further away from the interface you pass through regions where the waves augment and cancel - i.e. a standing wave pattern. Power flows to the right and to the left. You don't actually lose any Power.

Okay. Thank you. Now if the phase difference was zero, the resultant would still be a standing wave, but now there will be an antinode at the interface instead of a node as in the previous case. Is that right?

 

[sophiecentaur]

Right. It's due to the boundary conditions. A good example is the reflection of sound at the end of a pipe if it is closed or if it is open. You still get a standing wave but with a node or antinode at the end - depending.

 

[akhila_k]

Right. It's due to the boundary conditions. A good example is the reflection of sound at the end of a pipe if it is closed or if it is open. You still get a standing wave but with a node or antinode at the end - depending.

Thank you. That was really helpful.

 

[sophiecentaur]

Boundary conditions rule!