Plane polarised light is passed through a polaroid. On viewing through the polaroid we find that when the polaroid is given one complete rotation about the direction of light

Options

A. the intensity of light gradually decreases to zero and remains at zero
B. the intensity of light gradually increases to a maximum and remains maximum
C. there is no change in the intensity of light
D. the intensity of light varies such that it is twice maximum and twice zero

Answer

To solve the problem of how the intensity of plane polarized light changes as it passes through a rotating polaroid, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Polarized Light**:
- Plane polarized light consists of waves that oscillate in a single plane. When this light encounters a polaroid, it can either pass through or be absorbed depending on the orientation of the polaroid.

2. **Initial Setup**:
- Assume the plane polarized light is initially aligned with the axis of the polaroid (0 degrees). At this position, the intensity of the transmitted light is at its maximum.

3. **Intensity Variation with Rotation**:
- As the polaroid is rotated from 0 degrees to 90 degrees, the intensity of the transmitted light decreases. At 90 degrees, the light is completely blocked, and the intensity becomes zero.

4. **Continuing the Rotation**:
- If the rotation continues from 90 degrees to 180 degrees, the intensity starts to increase again. At 180 degrees, the polaroid is again aligned with the plane of polarization of the light, and the intensity reaches its maximum once more.

5. **Mathematical Representation**:
- The intensity of light transmitted through a polaroid can be described by Malus's Law:
\[ I = I_0 \cos^2(\theta) \]
where \(I_0\) is the initial intensity, and \(\theta\) is the angle between the light's polarization direction and the polaroid's axis.

6. **Summary of Intensity Changes**:
- As the polaroid rotates:
- From 0° to 90°, intensity decreases from maximum to zero.
- From 90° to 180°, intensity increases from zero back to maximum.

7. **Conclusion**:
- The intensity of light varies as it is rotated through the polaroid. It goes from maximum to zero and then back to maximum as the polaroid completes a full rotation of 180 degrees.

### Final Answer:
The intensity of light varies as it is rotated through the polaroid, going from maximum to zero and then back to maximum.

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