Understanding Phase Shift in Wave Light

[alchemist7]

phase shift in wave light??

when doing reflecton/refraction/transmission of wave light exercise,we must take phase shift into account. but in what situation there is a π phase shift ?

or other phase shift? i cannot apply this well!
help~

 

[Redbelly98]

When light reflects from a higher-index material, there is a π phase shift.

For other situations--reflection from a lower-index material, or any refraction--the phase shift is zero.

 

[derek e]

I think it can be useful to consider a medium with a "larger" index of refraction as a "thicker" string and a medium with a "smaller" index of refraction as a "thinner" string, then visualize the physics of a wave propagating down the two strings tied together, end-on-end.