The intensity of a sound wave gets reduced by 20% on passing through a slab. The

Question

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

Options:

A . 40%

B . 36%

C . 30%

D . 50%

Answer: Option B
:
B
Intensity after passing through one slab

I^{'} = [I - \frac{20}{100} \times I] = [I - \frac{1}{5}] = \frac{41}{5}

So, intensity after passing through two slabs

I "= [I - \frac{20}{100} \times I^{'}] = \frac{4 I^{'}}{5} = \frac{161}{25} ∴ % d e c r e a s e = [\frac{(I = - \frac{161}{5})}{I}] \times 100 = 36 %

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