MCAT Physics Question — Angle of Refraction
 by
 Jul 16, 2014
 MCAT Blog, MCAT Physics, MCAT Question of the Day
Light exits a Sylgard 184 silicone elastomer, index of refraction = 1.4, into air, index of refraction = 1, with an angle of incidence of 30°. What is the angle of refraction in the air on the other side of the Sylgard/air interface?
a) 30°
b) 45°
c) 60°
d) No refraction, the light is totally reflected internally.
Explanation
This problem is solved using Snell’s law: η_{1}sinθ_{1 }= η_{2}sinθ_{2}. On the MCAT, if you are asked to perform a Snell’s law problem, the angles will be angles with which you are familiar: think 30/60/90 triangles and 45/45/90 triangles. Sin30º=1/2, and 1.4 is roughly √2, therefore the right side of the equation is √2/2. The left side of the equation is sinθ_{1}. The angle for which the sin is √2/2 is 45°.
Total internal reflection occurs when the angle of refraction exceeds 90°, and sin90° = 1. For this problem, this would occur at an incident angle of 1.4sinθ_{i }= 1sin90°. Sinθ_{i} = 1/1.4 = 0.71. θ_{i} for total internal reflection is 45°.
a) 30°, incorrect, At an interface between two different indices of refraction the angle of refraction cannot equal the angle of incidence.
b) 45°, correct.
c) 60°, incorrect.
d) No refraction, the light is totally reflected internally. Incorrect, see explanation above.
Want more MCAT practice?
We’ve got options for every schedule and learning style!
From the best online MCAT course created by top instructors with 524+ MCAT scores to the most representative fulllength practice exams and private tutoring, we can custom tailor your MCAT prep to your goals!
Not sure which option is right for you? Schedule a free MCAT consultation with an MCAT Advisor using the form below. No obligation, just expert advice.
Search the Blog
Free Consultation
Interested in our Online MCAT Course, OneonOne MCAT Tutoring or Med admissions packages? Set up a free consultation with one of our experienced Senior Student Advisors.
Schedule NowPopular Posts

MCAT Blog What's on the MCAT?

MCAT Blog How to Review MCAT FullLengths
Free MCAT Practice Account
Need great MCAT practice?Get the most representative MCAT practice possible when you sign up for our free MCAT Account, which includes a halflength diagnostic exam and one of our fulllength MCAT practice exams.
Learn More
Submit a Comment