Polarisation Calculator: Malus Law, Two Polarisers and the Brewster Angle
Light through polarisers, and the Brewster angle.
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How this calculator works
Choose Malus's law, two polarisers or the Brewster angle.
Enter the intensity and angle, or the two refractive indexes.
The calculator gives the intensity or the angle.
Formulas used
- I = I_0\cos^2\theta
- I = \frac{I_0}{2}\cos^2\theta
- \tan\theta_B = \frac{n_2}{n_1}
Worked example
With the default numbers in the calculator above:
- Transmitted intensity: 75
- Fraction of the light transmitted: 0.75
Change the numbers in the calculator to see the full working, every step, for your own case.
A second worked example
A different case, with these numbers: What do you want to find? Unpolarised light through two polarisers.
- Intensity after the first polariser: 50
- Intensity after the second polariser: 37.5
- Fraction of the original light: 0.375
Common questions
What is Malus's law?
The intensity of polarised light after a polariser is the starting intensity times the square of the cosine of the angle between the light and the polariser.
What is the Brewster angle?
The angle of incidence at which the reflected light is fully polarised. It is the arctangent of the ratio of the refractive indexes.
Why do polarising sunglasses reduce glare?
Glare reflected off a flat surface is mostly polarised horizontally, and the glasses block that direction.
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Got a question about this? Ask an engineering question and get a plain-language answer with references.
Further reading: Any physics text (polarisation of light).
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