# ^Malus law

^**Malus law**

Let I_{0} be the intensity and ‘A’ the amplitude of the unpolarized light falling on the polarizer & θ be the angle between the pass axis of the polaroid & amplitude vector, then the component Acosθ, parallel to the pass axis (y) of polarizer passes through it & the component Asinθ, perpendicular to pass axis is blocked by the polarizer, thus the intensity of light transmitted by the polarizer is

I = k (A cosθ)^{2} = k A^{2} cos^{2} θ

or I = I_{0} cos^{2} θ [called Malus law

Actually the phase angle for a beam of unpolarised light can have any value from 0^{0} to 360^{0}. Now as the average value of cos^{2 }θ for the range 0^{0} to 360^{0 }is 0.5, thus the average intensity of light transmitted by a polarizer is only 0.5 I_{0}. Following observations can be explained on the basis of Malus law.

1. **Two polarizes with parallel pass axis (y & y)**

2. **Two polarizes with crossed pass axis (y & z)**