In this chapter, we will describe different properties of static charges, such as electric force, electric field and electric potential etc. We will also discuss some uses and safety measures of static electricity. The study of charges at rest is called electrostatics or static electricity.
13.1 PRODUCTION OF ELECTRIC CHARGES
If we run a plastic comb through our hair and then bring it near small pieces of paper, the comb attracts them (Fig.13.1). Similarly, amber when rubbed with silk, attracts the small pieces of paper. This property of attraction or repulsion between substances is due to the electric charges they acquire during rubbing.
We can produce electric charge by rubbing a neutral body with another neutral body. The following activities show that we can produce two types of electric charges through the process of rubbing.
Activity 13.1. Take a plastic rod. Rub it with fur and suspend it horizontally by a silk thread (Fig. 13.2). Now take another plastic rod and rub it with fur and bring near to the suspended rod. We will observe that both the rods will repel each other. It means during the rubbing both the rods were charged.
Activity 13.2. Now take a glass rod and rub it with silk and suspend it horizontally. When we bring the plastic rod rubbed with fur near to the suspended glass rod, we observe that both the rods attract each other (Fig. 13.3).
In the first activity, both rods are of plastic and both of them have been rubbed with fur. Therefore, we assume that charge on both rods would be of the same kind.
In the second activity, rods are unlike and their attraction implies that charges on two rods are not of the same kind but of opposite nature. These opposite charges are conventionally called positive charge and negative charge. During the process of rubbing negative charge is transferred from one object to another object.