Question

If a gun is fired from a distance, we see the flash of a gun first and the sound of gunshot is heard a little later. Give reason.

Answer 1

Hint: The speed of sound in the air is 330 m/s at room temperature. The speed of light in free space is 3, 00,000 km/s. comparing the speeds of light and sound, you will be able to answer this question.

Complete answer:
We know that the speed of sound in the air is 330 m/s at room temperature. It is even so less than the speed of light that we can neglect this speed if compared to speed of light. We know that the speed of light in free space is 3, 00,000 km/s.When we look at the gunshot from a distance, the flash of a gun travels with the speed of light that is 3,00,000 km/s and takes no time to reach our eye even if we are positioned at thousands of kilometers.

On the other hand, the sound of the gunshot travels in the air with a speed 330 m/s that is, it will take about 3 seconds to cover a 1 km distance. The time delay of 3 seconds can be easily noticed and thus, we see the flash of the gunshot before the sound of the gunshot is heard.

Additional information:
The sound is a longitudinal wave and longitudinal wave requires a material medium for the propagation. Therefore, the sound wave does not travel through a vacuum. The light is a transverse electromagnetic wave and the transverse wave does not require a material medium for its propagation and can travel through the vacuum.

Note: If we fire a bullet in the vacuum, we will not be able to hear any sound of the gunshot since the sound cannot travel through vacuum. But still we are able to see the flash of the gunshot since the light is able to propagate through the vacuum. The speed of the sound depends on the temperature and it decreases with increase in temperature.