Finding Light Shifting Distance: An Exercise in Refraction

[Bri]

A ray of light strikes a flat block of glass (n=1.5) of thickness 2.0 cm at an angle of 30 degrees with the normal. Find the distance the light is shifted.
I found the angle of refraction to be 19.471 degrees.
I figured I could find the horizontal distance traveled by rays going through at 30 and 19.471 degrees using tan(theta) = d/2.
Then I subtracted one distance from the other, and I get .446 cm, when, according to the book, I should get 3.88 mm.
What am I doing wrong?

 

[primarygun]

Sorry.

This is my first time to do this kind of question, so I don't have much information about what mistakes people always make. .
Perhaps, let me show you a picture and you may notice the mistake.
http://paintedover.com/uploads/show.php?loc=15&f=light.bmp

 

[ehild]

A ray of light strikes a flat block of glass (n=1.5) of thickness 2.0 cm at an angle of 30 degrees with the normal. Find the distance the light is shifted.
I found the angle of refraction to be 19.471 degrees.
I figured I could find the horizontal distance traveled by rays going through at 30 and 19.471 degrees using tan(theta) = d/2.
Then I subtracted one distance from the other, and I get .446 cm, when, according to the book, I should get 3.88 mm.
What am I doing wrong?

The lines of both the incident and emerging rays are parallel, and the shift of the light rays is characterized by the distance between those parallel lines. It is the length of the intersecting normal ("S" in the picture attached).

ehild

 

[primarygun]

Yes.I drew that line too but it is rather ugly. :p