Q147 / 180 · KCET 2011 · Physics
Two monochromatic light waves of amplitudes $3 \mathrm{~A}$ and $2 \mathrm{~A}$ interfering at a point have a phase difference of $60^{\circ}$. The intensity at that point will be proportional to
- A$5 A^{2}$
- B$13 A^{2}$
- C$7 A^{2}$
- Correct answerD$19 A^{2}$
Solution
Here, $A=\sqrt{A_{1}^{2}+A_{2}^{2}+2 A_{1} A_{2} \cos \theta}$
$$
\begin{gathered}
I=9 A^{2}+4 A^{2}+2 \times 3 A \times 2 A \times \frac{1}{2} \\
I=19 A^{2}
\end{gathered}
$$
Hence, the correct answer is option: 'D'.