As we know that wave of sound is a mechanical wave and its speed is given by

v =(γRT/M)

whereas the wave of light is an electromagnetic waveand its speed is given by

c =(1/εoμo)

So speed of sounddepends on temperature of air but speed of light doesn't.

Let S be the distance between the source of sound and reflector.
V be the velocityof sound in air.
t be the total time taken by the sound to travel from source to reflectorand back to the source.

2S = Vt
or,S = (Vt)/2

We can hear distinct sounds if they reach our ear after an interval of 0.1s or more
That is, t = 0.1s and V = 340 ms^-1

Therefore, S = (340 x 0.1)/2 = 17 m.
This is required minimum distance to hear an echo.

It is so because the speed of light (3 x 10⁸ m/s) is much greater than the speed ofsound (332 m/s) in a gas. Thus, light reaches immediately and sound reaches later tothe earth's surface.

The lower the density, the faster sound travels in a medium. The density of water vapour is less than that of air. So the density of air mixed with water vapour is less than that of dry air. Hence the speed of sound in moist air is greater than that in dry air(v1/ρ) . However, the density of water vapour is more than that of hydrogen, so the density of moist hydrogen is more than that of dry hydrogen. Consequently, the speed of sound in moist hydrogen is less than that in dry hydrogen.

Time taken (t) = 3 sec
Velocity of sound (v) = 332 m/s
Distance travelled (d) = ?

We know,

d = v x t = 332 x 3 = 996 m

Hence, the source of thunder is about 996 m far from the boy.

The drawback of Newton's formula for velocity of sound are:
1. The velocity of sound calculated from Newton's formula is279.9 m/s at N.T.P. Experimentally, they found that the velocity of sound in air at N. T. P is 332 m/s. Thus, there is a considerable difference between the value predicted by Newton’s formula and the experimental value.

2. Experimental value is 16% greater than the value given by the formula. Newton failed to satisfactorily explain the difference.

Laplace Correction:

Newton...

Velocities of sound in solids, liquids, and gases:

1. Solids: Sound travels fastest in solids. The velocity of sound in solids ranges from approximately 2000 m/s to 8000 m/s.

2. Liquids: Sound travels slower in liquids compared to solids. The velocity of sound in liquids is approximately 1000 m/s to 1500 m/s.

3. Gases: Sound travels slowest in gases. The velocity of sound in gases is around 343 m/s at room temperature.