Brewster Angle: Unknown Glass n
p-polarised light from air onto unknown glass. Find the incidence angle that extinguishes R_p and recover n = tan θ_B.
Goal
Determine n₂ from tan θ_B = n₂/n₁ with n₁ = 1 (air). θ_B is the angle of the R_p minimum.
Equipment
- p-polarised laser
- Unknown glass
- Goniometer
- Photodiode (R_p)
Experiment
Theory
At Brewster’s angle the reflected and transmitted rays are perpendicular and R_p → 0. The bench hides θ_B, n₂ and any “set Brewster” control. A live photodiode for p-polarised reflectance is the instrument.
Procedure
- The incident medium is air (n₁ = 1). The glass n₂ is hidden. You only change the incidence angle θᵢ.
- Watch the live p-photodiode R_p. Park at the minimum. The bench does not print θ_B.
- Record that θᵢ. The notebook computes n = tan θᵢ. Repeat the hunt at least 6 times.
- Take the mean of the n column and compare with the reference.
Conclusion
The mean n agrees with the hidden glass. Main uncertainties: discrete angle steps and judging the R_p minimum by eye.