Question

When a plastic comb is used to comb dry hair, what type of charge does the comb acquire?

A. Negative
B. Positive
C. Neutral
D. None of the above

Answer 1

Hint: Basically there are 4 fundamental forces in nature. Hence whatever the force we talk about, that must be derivative of one of these 4 fundamental forces. Now the friction force is a type of contact force which arises due to interaction between two objects. It comes under the category of electromagnetic fundamental force. This is responsible for charging the comb too.

Complete answer:
Usually for wet surface friction will be very less. But if the surface is too wet then friction might be more. Take an example of white marble. If the surface of white marble is too wet and if we place another white marble on it, it will be sometimes difficult to separate them or rub one on another due to friction.
But the dry surfaces have more friction. So if we comb the dry hair with the comb then due to more friction due to intermolecular interactions the electrons will transfer from the comb to the hair. Then comb will attain the positive charge due to the loss of electrons.
When we take this charged comb near small pieces of paper this comb will attract electrons from the paper towards it. Hence after combing, the comb will attract a bit of paper.

So, the correct answer is “Option B”.

Note:
When we comb the wet hair with the comb then the friction between the hair and the comb will be less due to wetness. Hence the charge obtained by the comb might not be enough to attract the paper pieces. That is the electrostatic force which arises between electrons and protons is responsible for attraction of paper pieces.