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How can a tag answer your phone without a battery?

A compatible passive NFC tag can obtain energy from a nearby reader's field and use it to communicate. The exchange depends on the reader and tag working together over a short distance.

4–5 min

Questions you could explore

  • How does a nearby reader supply enough energy for a passive NFC tag to respond?
  • How does the tag send information back while using power supplied by the reader?

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  • NFC ForumNFC Technology

    The NFC Forum explains operating modes and batteryless tags; some other NFC devices have their own power.

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Engineering and inventions

How GPS finds you, and fixes its clock

Your phone can work out where it is by listening to signals from far above Earth. But turning a signal's travel time into a distance also creates a clock problem: the receiver must account for its own timing error.

5–7 min

How GPS finds you, and fixes its clock

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Engineering and inventions

Across an ocean inside a fiber-optic cable

A message crossing an ocean can travel through glass fibers lying on the seabed. The light inside, the layers around it, and the equipment along the route each solve a different problem.

8–10 min

Across an ocean inside a fiber-optic cable

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Engineering and inventions

Bicycle gears and the distance of one pedal turn

Pedaling a bicycle once around in a low gear moves you a short distance with an easy push; pedaling once in a high gear sends you much farther down the road. The ratio of teeth on the front chainring to the rear sprocket explains how a simple chain drive trades pedaling force against distance traveled.

3–5 min

Bicycle gears and the distance of one pedal turn

Engineering and inventions3–5 minPedaling a bicycle once around in a low gear moves you a short distance with an easy push; pedaling once in a high gear sends you much farther down the road. The ratio of teeth on the front chainring to the rear sprocket explains how a simple chain drive trades pedaling force against distance traveled.

How can a tag answer your phone without a battery? | Speech Topic | speaking.app