THERE IS AN ACTIVITY IN THE BOOK ; BY RUBBING REFILL ON A POLYTHENE THE PAPER PARTICLES STUCK TO IT . A SIMILAR ACTIVITY WAS BY RUBBING SCALE ON YOUR HEAD THE PAPER PARTICLES STUCK TO IT ; BUT WHEN THE HAIRS ARE WET THEN THE PARTICLES DOESN'T STUCK . WHY?

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Solution

When we rub a scale with dry hair repeatedly, due to friction, the loosely held electrons in our hair are transferred to the scale. Buildup of static charge takes place. So, hair becomes positively charged and the scale acquires a negative charge. This negatively charged scale can now attract objects that carry an excess of positive charge in them, like bits of paper.
But wet hair has a coating of water (or any other liquid) on them. This reduces the friction between the hair and scale and as a result no electron flow takes place. Thus no static charges develop. The scale would never get negatively charged and consequently wouldn't attract paper particles.

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