Question

Suppose we rotate the second sheet in Fig. 33-15a, starting with the polarization direction aligned with the y axis$\left(\theta =0^0\right)$and ending with it aligned with the x-axis$\left(\theta =90°\right)$. Which of the four curves in Fig. 33-26 best shows the intensity of the light through the three-sheet system during this$\mathbf{90}\mathbf{°}$rotation?

Short answer

The curve ‘c’ best shows the intensity of light emerging from the system.

Step-by-step solution

The given data

The polarization direction of the second sheet changes from initially aligned with y axis $\left(\theta =0^0\right)$ to finally aligned with x axis$\left(\theta ={90}^0\right)$ .

Understanding the concept of intensity of polarization

By passing it through a polarizing filter or other polarizing substance, light can be made polarized. The cosine-square rule can be used to calculate the intensity of unpolarized light after it has gone through a polarizing filter. Here, we must apply the polarization principle utilizing polarizing sheets. The polarizing direction also shifts as we rotate the sheet because of its angle with the incident rays. As a result, the intensity of that sheet likewise changes.

Calculation for the curve representing best intensity of light through the three-sheeted system

The polarization direction of second sheet is aligned with the y axis initially. So, the direction of polarization for first two sheets will be same and the third sheet crossed with them. Hence, there will be no light emerging resulting zero intensity.

In a similar way, as finally the second sheet has polarization direction aligned with x axis, crossed with first polarizing sheet, resulting zero intensity.

It means the curve which is at zero at initial and final position, is the best representation of the intensity of light emerging from the system.

Hence, the curve ‘c’ best represents the intensity of the light emerging through the system.