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An ultrasonic distance sensor works like a bat. It sends a sound too high for us to hear and listens for the echo. Sound travels about 34 cm every millisecond, but it has to go to the object AND come back, so the object is 34 ÷ 2 = 17 cm away for every millisecond of echo time. An echo after 4 ms means 17 × 4 = 68 cm. A robot can use this to stop before it hits a wall.
✓ You passed this lesson’s test.
Half the echo path — “the sound goes there and back, so the distance is half of what the sound travels”
Use it for: Obstacle-avoiding robots, parking sensors, bats and dolphins in science, and speed–distance–time sums.
Check: 68 × 2 = 136 = 34 × 4 ✓
▶ Watch it animatedWork it out in your head or on paper, type the answer and press Check. Stuck? Press “Show me how”.
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20 questions. Check each answer, then go to the next one. Get 16 or more right to pass.
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