Question

Two interfering wave (having intensities are 9I and 4I) path difference between them is 11 λ. The resultant intensity at this point will be

• A. I
• B. 9 I
• C. 4 I
• D. 25 I

Answer 1

Answer: (D)

25 I

Answer 2

Path difference $\Delta = \frac{\lambda}{2\pi} \times \varphi$

⇒ $\frac{2\pi}{\lambda} \times 11\lambda = 22\pi$ i.e. constructive interference obtained at the same point

So, resultant intensity

$I_{R} = (\sqrt{I_{1}} + \sqrt{I_{2}})^{2} = (\sqrt{9I} + \sqrt{4I})^{2} = 25I$.