Question

The sound produced by a thunderstorm is heard 10 s after the lightning is seen. Calculate the approximate distance of the thunder cloud. (Given the speed of sound = 340 m s^–1.)

Answer 1

Let the distance of thunder cloud from observer be x m.

Now, speed of light = 3 x 108 ms⁻¹

Speed of sound = 340 ms⁻¹

Time is taken by the light to reach the observer,

`"t"_"l" = "x"/(3 xx 10^8) "S"`

Time is taken by the sound to reach the ``observer,

`"t"_"l" = "x"/340 "S"`

Given, t_{8 −} t₁ = 10s 

`"x"/340 - "x"/(3 xx 10^8) = 10` or `"x"(1/340 - 1/(3 xx 10^8)) = 10`

`"x"/340 = 10` (∵ 3 × 10⁸ >>> 340, ∴ `1/340` >>> `1/(3 xx 10^8)`)