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Mystery #1Tier 1electricity / circuits

Why does a torch only work when everything is joined up just right?

Slide a torch's switch and a bright beam leaps out. But leave one tiny thing loose, a battery in the wrong way, a bulb not quite screwed in, and nothing happens at all. Every piece is still there, still full of power. So why does the torch stay dark until it is all joined up just right?

A torch shining a bright beam of light onto a log in the dark
Photo: Rosaparks · CC BY-SA 4.0 · via Wikimedia Commons

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