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

Options

A. `40%`
B. `36%`
C. `30%`
D. `50%`

Answer

B

Explanation

Intensity after passing through one slab
`I'=[I-(20)/(100)xxI]=[I-(I)/(5)]=(4I)/(5)`
So, intensity after passing though two slabs
`I''=[I'-(20)/(100)xxI']=(4I')/(5)=(16I)/(25)`
`%` decrease`=[((I-(16I)/(25)))/(I)]xx100=36%`