# Refraction of Light question assistance needed

As revision for my upcoming physics exam, I'm doing an old exam paper from a previous year of the course, for which the answers aren't published. However, I'm stuck on a basic angle of refraction question:
"A light ray makes an angle of 35degrees to the surface of an oil layer. [A diagram is attached, which shows the light ray travelling through air until it hits the oil surface]. The air's n=1.00, and the oil''s n=1.47. What is the angle of refraction of the light ray in the oil?"

It's a multichoice answer, and the answers are A) 35degrees, B) 56.1degrees, C) 55.9degrees, D) 33.9degrees, and E) 67.7.
However when I use the n1*sin(theta1) = n2*sin(theta2) method, my answer is always equal to 22.97degrees? Which is equal to none of the multichoice answer values? And because there are no published answers, I can't check the correct answer.
Have I done something wrong? Or is there a mistake in the exam paper? Thank you for any and all help!
[P.S. my calculator is definitely set in degrees.]

Relevant equations:
n1*sin(theta1) = n2*sin(theta2)

The attempt at a solution:
1 * sin(35) = 1.47 * sin(theta2), therefore sin-1 (sin(35)/1.47) = theta2 = 22.97degrees.

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andrevdh
Homework Helper
Try 90o - 35o as the incident angle.
The incident angle for Snell's law is measured with respect to the normal to the surface.

Try 90o - 35o as the incident angle.
The incident angle for Snell's law is measured with respect to the normal to the surface.
Thank you very much! A dumb mistake on my part; you've saved me from embarrassing myself in front of my lecturer when I went to ask him for help, and the extra info at the bottom was also very helpful, thank you again!

andrevdh
Homework Helper
Don't be afraid to make mistakes or ask questions (and hopefully do not break anything in the process). That is (mostly) how we learn.