Question

At a time when it is cloudy, there may be frequent thunder and lightning. You hear the sound of thunder after observing the lightning stroke. Can you answer why this happens? Measure this time interval using a time watch. Calculate the distance of the nearest point of lightning ( speed of sound in air = 346 ms^-1)

Answer 1

Step 1: Reason why light appears faster than sound.

1. Lightning and thunder occur simultaneously when two clouds collide with each other.
2. Both thunder and lightning take place at the same time.
3. For an observer on the earth, the sound of thunder hears after observing the lightning stroke.
4. Because light travels faster than sound.
5. Light travels at a speed of $3\times {10}^8\frac{m}{s}$
6. Sound travels with a speed of $346\frac{m}{s}$
7. This is the reason why light appears first before hearing the sound.

Step 2: Calculation of distance of the nearest point of lightning.

Using a stopwatch we can measure the time intervals.

Suppose, t = 2 sec

Consider the equation of distance,

$$\begin{gathered} Dis\tan ce=speed\times time \\ =346\times 2 \\ =692m \end{gathered}$$

Hence, if the time interval is 2 sec, the distance of the nearest point of lightning is 692 m.