Malus' law is an important experiment to understand the polarization property of light and demonstrate the transverse characteristic of electromagnetic waves. This App is served as a photometer to automatically measure the illuminance of a polarized light through the second polarizer. The diagram of illuminance as a function of (cosθ) ^ 2 (θ is the angle between two polarizers) is auto-generated by the App accompanying with a linear fitting function and the regression coefficient.

Required Apparatus:
A laser point (as a light source)
A DIY module for experiment (comprising of two polarizers, adjustable holders)
A smartphone with “Mobile PhysLab: Malus Law” App

Procedures:
1. Construct the DIY module for experiment.
2. Set up the laser point, the DIY module for experiment, and the smartphone.
3. Determine the angle between two polarizers.
4. Setup the Malus ’Law App and rotate the second polarizer to get different θ in the range 0 ° to 90 ° to measure the illuminance against different values ​​of θ.
5. Switch to Chart View in the App and check the functional relation between illuminance and (cosθ) ^ 2.


Authors:
Yuanxi Li
Shih-Sin Jhang
Bing-Shiou Tsai
Yao-Chen Hung (洪 耀 正, Advisor)

Mobile PhysLab, Feng Chia University, Taichung, Taiwan