Electrostatics, Grade 10 Physics 1/ Introduction Electrostatics is the study of electric charge which is static (not moving). 2/ Two kinds of charge All objects surrounding us (including people!) contain large amounts of electric charge. There are two types of electric charge: positive charge and negative charge. If the same amounts of negative and positive charge are brought together, they neutralise each other and there is no net charge. Neutral objects are objects which contain positive and negative charges, but in equal numbers. However, if there is a little bit more of one type of charge than the other on the object then the object is said to be electrically charged. The picture below shows what the distribution of charges might look like for a neutral, positively charged and negatively charged object. 3/ Unit of charge Charge is measured in units called coulombs (C). A coulomb of charge is a very large charge. In electrostatics we therefore often work with charge in microcoulombs (1 µC = 1 × 10$^{−6}$C) and nanocoulombs (1 nC = 1 × 10$^{−9}$C). 4/ Conservation of charge Objects can become charged by contact or by rubbing them. This means that they can gain extra negative or positive charge. Charging happens when you, for example, rub your feet against the carpet. When you then touch something metallic or another person, you will feel a shock as the excess charge that you have collected is discharged. Important: Charge, just like energy, cannot be created or destroyed. We say that charge is conserved. When you rub your feet against the carpet, negative charge is transferred to you from the carpet. The carpet will then become positively charged by the same amount. Another example is to take two neutral objects such as a plastic ruler and a cotton cloth (handkerchief). To begin, the two objects are neutral (i.e. have the same amounts of positive and negative charge.) Now, if the cotton cloth is used to rub the ruler, negative charge is transferred from the cloth to the ruler. The ruler is now negatively charged and the cloth is positively charged. If you count up all the positive and negative charges at the beginning and the end, there are still the same amount. i.e. total charge has been conserved ! Xem thêm: Physic 10.VIII Electrostatics High School Students Studying the Sciences Physics