Question

An analyser examines two adjacent plane-polarised beams A and B whose planes of vibration are mutually perpendicular. In one position of the analyser, beam B shows zero intensity. From this position, a rotation of 30${}^0$ shows the two beams as matched in intensity. The intensity ratio I_{A}/I_{B} of the two beams is

• A. $\sqrt{3}$
• B. $1/3$
• C. $1/\sqrt{2}$
• D. $\sqrt{5}$

Answer 1

The correct option is B $1/3$

$I_{A}co{s}^{2}30=I_{B}co{s}^{2}60$
$I_A\frac{3}{4}=I_B\frac{1}{4}$
$\frac{I_A}{I_B}=\frac{1}{3}$
option $B$ is correct