Physics · Oct / Nov 2017 · Paper 11 · Question 20

A solid plastic cylinder is immersed in a liquid of refractive index 1.4. Light travelling in the plastic cylinder strikes the inside surface at an angle of incidence of 70°. The light undergoes total internal reflection. What are the values of the critical angle in the plastic and the refractive index of the plastic?

1. Acritical angle in plastic: greater than 70°; refractive index of plastic: greater than 1.4
2. Bcritical angle in plastic: greater than 70°; refractive index of plastic: less than 1.4
3. Ccritical angle in plastic: less than 70°; refractive index of plastic: greater than 1.4
4. Dcritical angle in plastic: less than 70°; refractive index of plastic: less than 1.4

As printed in the paper