Light travels through ethanol and strikes the surface of plexiglass at an angle of 48^o. At what angle does it continue through?

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n₁sinθ₁ = n₂sinθ₂

1.36sin(48°) = 1.51sinθ₂

sinθ₂ = 1.36 x 0.7431 /1.51 = 0.669

θ₂ = sin⁻¹(0.669) = 42°

Note you can 'guess' the answer without any calculations. The angle must reduce (be less than 48°) because we are entering a material of higher refractive index.

And the change in angle will be small because the refractive indices are quite similar. So 42° is the natural guess if you are short of time in an exam'....Show more

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