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Q1 (CAPF/2021) Science & Technology › Basic Science (Physics, Chemistry, Biology) › Waves and acoustics Answer Verified

The time elapsed between viewing a lightning flash and hearing the thunder of a cloud is 10 s. If the speeds of sound and light in the air are 330 m/s and 3 × 108 m/s respectively, how far away is the storm?

Result
Your answer: —  ·  Correct: B
Explanation

The distance to a storm can be calculated using the time lag between seeing lightning and hearing thunder. Light travels at approximately 300,000,000 m/s, making its arrival almost instantaneous for terrestrial distances [1]. Sound, however, travels much slower at approximately 330 m/s in air [1]. To find the distance, the formula Distance = Speed × Time is applied [2]. Given the speed of sound is 330 m/s and the time elapsed is 10 seconds, the calculation is 330 m/s × 10 s = 3300 meters. While light also takes a finite time to travel, its contribution to the 10-second delay is negligible (about 0.000011 seconds for this distance). Therefore, the storm is approximately 3300 meters away, which aligns with the standard 'flash-to-bang' method used in meteorology to estimate proximity to lightning strikes.

Sources

  1. [1] Environment and Ecology, Majid Hussain (Access publishing 3rd ed.) > Chapter 8: Natural Hazards and Disaster Management > Tunderstorms and Hails in India > p. 52
  2. [2] https://www.grc.nasa.gov/www/k-12/airplane/sound2.html
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