Question

How will you detect plane polarized light by polaroid?

Hint:

The key to this detection method is the rotation of the analyzer. The signature of plane polarized light is the complete extinction (intensity becomes zero) at two specific orientations of the analyzer, 180\(^\circ\) apart.

Answer 1

Step 1: Understanding the Concept:
Plane polarized light is light in which the electric field vibrations are confined to a single plane. Unpolarized light has vibrations in all possible planes perpendicular to the direction of propagation. A Polaroid is an optical filter that has a "transmission axis" and only allows the component of light polarized parallel to this axis to pass through. This property can be used to analyze an unknown light beam.

Step 2: Key Formula or Approach:
The detection method is based on Malus's Law, which describes the intensity of light transmitted through a Polaroid (acting as an analyzer): \[ I = I_{max} \cos^2\theta \] where \(I\) is the transmitted intensity, \(I_{max}\) is the maximum transmitted intensity (when the analyzer's axis is aligned with the light's polarization), and \(\theta\) is the angle between the analyzer's transmission axis and the plane of polarization of the incident light.

Step 3: Detailed Explanation:
The procedure to detect plane polarized light is as follows:
\begin{enumerate} \item Setup: Place a Polaroid, which will serve as an analyzer, in the path of the light beam being tested. \item Action: Rotate the Polaroid analyzer slowly through a full 360\(^\circ\) rotation about the axis of the light beam. \item Observation: Observe the intensity of the light transmitted through the Polaroid. \item Conclusion: \begin{itemize} \item If the light is plane polarized, the intensity of the transmitted light will vary significantly during the rotation. It will change from a maximum value to a minimum value of zero, twice in one full rotation. The intensity is maximum when the Polaroid's axis is parallel to the light's polarization plane (\(\theta = 0^\circ\)) and zero when it is perpendicular (\(\theta = 90^\circ\)). \item If the light is unpolarized, the intensity of the transmitted light will remain constant as the Polaroid is rotated. \item If the light is partially polarized, the intensity will vary between a maximum and a non-zero minimum during rotation. \end{itemize} \end{enumerate}

Step 4: Final Answer:
To detect plane polarized light, one must rotate a Polaroid in its path. If the transmitted light intensity varies and becomes zero at two positions during one complete rotation, the incident light is confirmed to be plane polarized.