15.1 Electric Charge
When a plastic comb is rubbed through dry hair and brought near small pieces of paper, it attracts them. Similarly, an amber rod rubbed with silk attracts small pieces of paper. We often experience a shock when we touch a metal doorknob after sliding across a car seat or walking on a synthetic carpet. In each case, the electrostatic force resulting from electric charges is in action.
lightbulbElectric charge is an intrinsic property of matter that causes attraction or repulsion between objects. The SI unit of charge is the coulomb (C).
There are two types of electric charges: positive and negative. This can be demonstrated by rubbing a glass rod with silk (positive charge) and a plastic rod with wool or fur (negative charge). When two glass rods are brought close, they repel each other because both are positively charged. When two plastic rods are brought close, they repel each other because both are negatively charged. When a glass rod and a plastic rod are brought close, they attract each other because they have opposite charges.