Question

The intensity of sound gets reduced by $20\text{\%}$ on passing through a slab. The reduction in intensity on passage through two consecutive slabs is

• A. $40\text{\%}$
• B. $36\text{\%}$
• C. $30\text{\%}$
• D. $50\text{\%}$

Answer 1

The correct option is B $36\text{\%}$

Let $I$ be the initial intensity of the sound.

Let $I_1$ and $I_2$ be the intensities of the sound after passing through one and two slabs respectively.

As intensity reduces by $20$ % of the incident sound on passing through a slab.

Thus $I_1=80$ % of $I⟹I_1=0.8I$

Now $I_2=80$ % of $0.8I=0.64I$

Thus percentage reduction in intensity $=\frac{I-I_2}{I}\times 100=\frac{I-0.64I}{I}\times 100=36$

$⟹$ Intensity reduces by $36$ %.