Question

A thunder is heard 4 seconds after the lightning. At what distance the lightning occurs?
A. 1480 m
B. 1380 m
C. 2380 m
D. 1000 m

Answer 1

Hint: It is a very common phenomenon that we see flash in the sky first and then we hear the sound. This happens because the speed of light is greater than the speed of sound. Light is an electromagnetic wave and all such waves travel with the speed $3\times {{10}^{8}}m/s$ while sound is not an electromagnetic wave. Sound is a longitudinal wave and its speed depends upon the medium in which it travels. In vacuum it moves with the speed $340m/s$.

Complete step by step answer:
We are given that the thunder is heard after 4 seconds, $t=4s$ and we know the speed of sound is $v=340m/s$. So, we can make use of the formula: $d=vt$, to find out the distance at which the lightning occurs.
$d=vt$
$\Rightarrow d=340\times 4$
$\therefore d=1360m$
Hence, the distance the lightning occurred is 1360 m. This is close to 1380 m mentioned in the options.

So, the correct option is B.

Additional Information:
Light or visible light is an electromagnetic radiation. An electromagnetic radiation is produced by an accelerated charged particle or by a charged particle which is in vibration and electromagnetic rays have their unique properties which makes them stand out of all the radiations that exist in nature.

Note: While solving such problems we use simple equations of motions and here we have used the relationship between speed, distance and the time. Speed of light is constant and we were given with the time. So, we have easily just found out the distance covered by the light in the given interval of time. Also, the options given, none of them matched perfectly and so we have considered the nearest quantity.