►All matter is made up of atoms and/or molecules. Although the materials are electrically neutral, they do contain charges; but their charges are exactly balanced.
►To electrify a neutral body, we need to add or remove one kind of charge. When we say that a body is charged, we always refer to this excess charge or deficit of charge.
►In solids, some of the electrons, being less tightly bound in the atom, are the charges which are transferred from one body to the other. A body can thus be charged positively by losing some of its electrons.
►Similarly, a body can be charged negatively by gaining electrons.
►When we rub a glass rod with silk, some of the electrons from the rod are transferred to the silk cloth. Thus the rod gets positively charged and the silk gets negatively charged.