Question

In the Young's double slit experiment, the interference pattern is found to have an intensity ratio between bright and dark fringes as $9 .$ This implies that

• A. the intensities at the screen due to two slits are 5 units and 4 units respectively
• B. the intensities at the screen due to two slits are 4 units and 1 unit respectively
• C. the amplitude ratio is 3
• D. the amplitude ratio is 2

Answer 1

Answer: (B)

As, $\frac{I_{\max }}{I_{\min }}=\frac{(a+b)^{2}}{(a-b)^{2}}=9$
or $\frac{a +b}{a-b}=3$
or $3 a-3 b=a +b$
or $2 a=4 b$
$\therefore \frac{I_{1}}{I_{2}}=\frac{a^{2}}{b^{2}}=\frac{4 b^{2}}{b^{2}}=4: 1$