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If one rubs a neutral glass rod with cat fur will cause it to have excess negative charge in low humidity, but not in highly humid conditions. Why not? How does the water neutralise the rod?

Why does charging / discharging happen in low humidity, but not in highly humid conditions?

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  • $\begingroup$ I guess that "humidity" is a some sort of lubrificator, so the charge separation is less effective while rubbing. $\endgroup$ Jul 20 '18 at 13:39
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In high humidity, some water will condense on the surfaces of a glass rod and a fur, which may affect their triboelectric properties. As a result, when they are rubbed against each other, the charging may not be as effective. In this scenario, the water does not neutralize the rod, but just prevents it from being effectively charged in the first place.

Let's consider a different scenario, when you charge the rod in a dry room and then move it to a humid room. First, some water will condense on the surface of the rod. If the condensation level is high enough, the water may form a continuous layer and, by dissolving some minerals present on the surface of the rod, become slightly conductive. In this case, the charge will flow off the rod into your body and, thus, effectively, neutralize the rod.

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When humidity is low, higher static charges are generated. Increased humidity limits static build-up because it's a conductor.

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