Question

The intensity of sound wave gets reduced by 20% on passing through a slab. The reduction in intensity onpassing through two consecutive slabs is

• A. 40%
• B. 36%
• C. 30%
• D. 50%

Answer 1

The correct option is B 36%

Let initial intensity is I. On first passes the intensity loss will be 20% of I. So $I_1=0.8I$.
On second passage the loss will be 20% of 0.8 I.
$\frac{20}{100}\times \frac{8}{10}I=0.16I$
So the final intensity will be $0.8I-0.16I=0.64I$.
So loss will be $\frac{0.64I-I}{I}\times 100$
36%