Physics Question #308

Edward Driedger, a 11 year old male from the Internet asks on December 17, 1997,

How do touch lamps work? If one person touches the touch pad and someone else taps his other hand, will the light still react?

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The answer

Tim Collings answered on December 17, 1997

Most touch lamps work using a capacitive sensor. The dielectric field strength changes when a foreign object is brought in proximity with the switch. The capacitance is altered according to C = e*A/d where e is the dielectric, A is the cross-sectional area of the capacitor plates and d is the distance between plates.

The reason why a second person can touch the first person to make the switch work is because this, too, changes the dielectric field strength enough to actuate the switch.

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