Technology · Level 1 · 172 words

How Your Phone Knows Where You Are

Original passage © Studio AM, written for Fluency.

Open a map on your phone and a blue dot appears. The phone did not ask anyone where you are. It worked it out, and it did so by listening to clocks in space.

High above the earth, satellites circle in fixed paths. Each one carries a very accurate clock and sends out a steady signal. The signal says two things: which satellite is speaking, and the exact time the message left. The signal travels at the speed of light, which is fast but not instant. Your phone reads the time in the message, compares it with the time now, and turns that tiny gap into a distance.

One distance is not enough. Knowing you are 20,000 kilometres from one satellite places you somewhere on a huge sphere. A second satellite narrows it. With four, the phone can fix your position and correct its own cheap clock at the same time. This is also why the blue dot struggles indoors. The signals are faint, and thick walls are enough to lose them.

Comprehension questions

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4 questions
1. According to the passage, what two things does a satellite's signal say?

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B. Which satellite is speaking, and the exact time the message left.
The second paragraph lists them directly: which satellite is speaking, and the exact time the message left.

2. What is the passage mainly explaining?

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C. How a phone works out its position from satellite signals.
Every paragraph builds the same explanation: signals carry a send time, the phone turns the gap into a distance, and several distances fix a position.

3. The passage suggests that if the speed of light were instant, this method would

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A. no longer work, because there would be no time gap to measure
The phone turns the tiny gap between the send time and now into a distance. The text points out that light is "fast but not instant." With no gap, there would be nothing to measure.

4. In this passage, "faint" means

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D. weak and hard to pick up
The word explains why the dot struggles indoors, alongside thick walls that lose the signals. A weak signal is the reason. Distance alone is not the point, since the satellites are always far away.

Source: Written for Fluency. Original passage © Studio AM, written for Fluency.