Answers for the Teacher Only

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What Do You Think?

The delay is caused by the travel-time of light. Although light moves extremely fast, its speed is finite and has the value 3 X 10⁸ m/s. Communications satellites sit in orbits over a point on the Earth, at a distance of about 4 X 10⁷ m. Consequently, a message sent to a communications satellite and back to Earth would require 2 X 4 X 10⁷/(3 X 10⁸) s, which is about 0.3 s.

Suppose a TV reporter asks a question. It takes 0.3 s for the end of that question to reach the person interviewed, elsewhere on Earth. Then it takes another 0.3 s for the beginning of the reply to reach the reporter, plus the delay between hearing the end of the question and beginning the reply. Since human reaction time is about 0.5 s, the total delay between the end of the question and the beginning of the answer, as seen on TV, is about one second.