十万个为什么·科学启蒙30篇（2）
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How Do Touchscreens Actually Work?
触摸屏究竟是如何工作的？
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Most smartphones use capacitive touchscreens, which rely on the fact that your finger conducts electricity better than air or glass.
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A grid of transparent electrodes sits beneath the screen surface, and a constant low-voltage charge flows across it evenly.
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When your finger touches the screen, it draws a tiny amount of current from nearby points, changing the local electrostatic field.
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The device detects these changes in capacitance at multiple points and calculates the exact touch location using algorithms.
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Unlike older resistive screens — which needed pressure to press two layers together — capacitive screens respond to light taps and even gloved fingers with special conductive thread.
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Multi-touch capability allows zooming, rotating, and swiping because the system tracks several contact points simultaneously.
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Water or metal objects can confuse capacitive sensors, which is why screens sometimes misbehave near wet hands or metal surfaces.
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Future screens may use ultrasound or optical sensors to detect hovering gestures without any physical contact at all.