# Static electricity

Electrostatics > Static electricity

Static Electricity is produced by a concentration of Negative or Positive Electric Charges. Similar Charges Repel each other, but Opposite Charges Attract each other, Figure 1.

Figure 1: Similar Charges Repel each other and Opposite Charges Attract each other

Objects ordinarily have equal numbers of Positive Charges and Negative Charges. If there is slight imbalance in the numbers of Charges on the object, the object is charged.

Negative Charges are easily torn away from some materials, Fur and Hair for example. On the other hand, Negative Charges are firmly held on some materials, Plastic for example. If we rub the Plastic Rod with the Fur, Negative Charges are transferred from the Fur to the Rod. The Rod is negatively charged and the Fur is positively charged.

Electroscope is an electrical instrument for indicating the Electric Charge, Figure 2(a). If we touch with a charged object the top of the Electroscope, the Electroscope Needle and Post receive Similar Charges, the Needle and the Post repel each other, Figure 2(b).

Figure 2(a): Electroscope

Figure 2(b): Electroscope Needle and Post receive Similar Charges, the Needle and the Post repel each other

The charge distribution on an object can be changed by other charged object. This can be done by touching with the negatively charged Plastic Rod the top of the Plastic Case filled with Styrofoam Balls, or rub the Case with the Fur, Figure 3. Initially, the net charge on the Styrofoam Balls is zero. The Positive and Negative Charges are equally distributed on the Styrofoam Balls - Neutral Stage, Figure 4. When the Plastic Rod touches or the Fur rubs the Plastic Case, a new charge redistribution is induced on the Styrofoam Balls by the negatively charged Plastic Case. Then, the Styrofoam Balls are attracted, Figure 5.

Figure 3: Plastic Case filled with Styrofoam Balls

Figure 4: The Positive and Negative Charges are Equally Distributed on the Styrofoam Balls

Figure 5: A new Charge Redistribution is Induced on the Styrofoam Balls by the Negatively Charged Plastic Rod

How to make Rod becomes Positively Charged? If we rub the Plastic Rod with Silk, Negative Charges will be transferred from Rod to the Silk. The Rod becomes Positively Charged.

There are many examples of Static Electricity in daily life. Do you notice that the comb attracts your hair when you are combing your hair during the dry weather? Do you hear the sound of "pop" when you take off your woolen sweater during the winter?

Electrostatics > Static electricity