In an ordinary battery, chemical reactions force electrons to accumulate on one side of the battery (the anode), where the mutual repulsion of these like-charged particles means they’re primed to flee at the first opportunity. When you complete an electrical circuit by pushing an “on” button or flipping a switch, you free the pent-up electrons, allowing them to flow out of the anode, pass through a device—bulb, laptop, phone—and finally return to the battery’s other side (the cathode). Commonplace though batteries are, they are utterly ingenious. They store energy in a crowded collection of
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