How many times in one second can a light beam circle the Earth?

How many times in one second can a light beam circle the Earth?

• A. 7.5
• B. 1
• C. 10
• D. 0.5

Answer: (A)

Think of how many times light can travel around the Earth in one second by comparing distance to speed. Light travels about three hundred thousand kilometers every second. The Earth’s circumference is about forty thousand kilometers. Time for one full circumnavigation is roughly forty thousand divided by three hundred thousand, which is about 0.133 seconds. In one second, that means light can complete about one second divided by 0.133 seconds per loop, which works out to around seven and a half loops. So a light beam could circle the Earth roughly seven and a half times in one second. This is a simple rounded estimate that ignores atmospheric effects and the fact that Earth isn’t a perfect circle.

Think of how many times light can travel around the Earth in one second by comparing distance to speed. Light travels about three hundred thousand kilometers every second. The Earth’s circumference is about forty thousand kilometers. Time for one full circumnavigation is roughly forty thousand divided by three hundred thousand, which is about 0.133 seconds. In one second, that means light can complete about one second divided by 0.133 seconds per loop, which works out to around seven and a half loops. So a light beam could circle the Earth roughly seven and a half times in one second. This is a simple rounded estimate that ignores atmospheric effects and the fact that Earth isn’t a perfect circle.