Revered members,
While explaining the interference in thin film with this attachment, my book says the following line
When a ray is reflected at the boundary of a rarer to denser medium, a path change of λ/2 occurs for the ray BC. There is no path difference due to transmission at E.
I can't understand this, because in my attachment, E is also reflected at the boundary of a rarer to denser medium.

 

In your diagram ray reflected BC is actually ray ABC.
That is it comes from A and is (the part) reflected at B that proceeds to C.

As you note it its path is entirely within the less dense medium and is (the part of ray AB reflected at the boundary with the more dense one.

Now ray EF is actually ray ABDEF.
That is it comes from A, is (the part) refracted at B into the more dense medium, and then is (the part) reflected at D back to E within the more dense medium, and finally is (the part) refracted at E back into the less dense medium.

 

Thanks a lot studiot