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I've gotten pretty good with the math when it comes to rays/optics, but I'm still missing some of the vocabulary. When a question says "A light ray is incident on glass at $30^{\circ}$" does this mean this is the angle from the normal? Here's the context of the question I'm asking this about:

A sheet of glass has n$_{red}$=1.52 and $n_{violet}$=1.55. A narrow beam of white light is incident on the glass at 30°. What is the angular spread of the light inside the glass?

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    $\begingroup$ In general, unless otherwise stated, angles are measured from the normal. $\endgroup$
    – Farcher
    Commented May 21, 2017 at 20:38
  • $\begingroup$ I can confirm this is the case. See the definitions of terms and the diagram here: en.wikipedia.org/wiki/Ray_(optics)#Special_rays $\endgroup$
    – userManyNumbers
    Commented May 21, 2017 at 21:19
  • $\begingroup$ Yes it's incident angle wit Normal If he said incident on surface will be incident angle If said incident with surface will be The other angle which with surface of plane and will make 90 - angle $\endgroup$
    – AHMED ABD ELLATIFFE
    Commented May 15, 2022 at 7:39

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It just means that the path of the light intersects the plane of the glass. The angle between this ray and the perpendicular or normal to the surface is the angle of incidence. The reflected ray corresponding to a given incident ray, is the ray that represents the light reflected by the surface.

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Yes it does mean the angle with the normal.. in this case an incident angle of 30 degrees would mean the incident ray (the light ray flaling on the reflecting surface) makes as angle of 30 degrees with the normal

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