1.2.1 GOLD LEAF ELECTROSCOPE

gold-leaf electroscope is the simple apparatus to detect charge on the body.
 construction= It consists of a vertical metal rod housed in a box, with two thin gold leaves attached to its bottom end.
working= When a charged object touches the metal knob at the top of the rod, charge flows on to the leaves and they diverge. The degree of divergence is an indicator of the amount of charge.The white paper strips is used to explain the working of the apparatus. We fold the strips into half so that we make a mark of fold.We  open the strip and iron it lightly with the mountain fold up.We hold the strip by pinching it at the fold.We notice that the two halves move apart.This shows that the strip has acquired charge on ironing. When we fold it into half, both the halves have the same charge. Hence they repel each other. The same effect is seen in the leaf electroscope.
 On charging the curtain rod by touching the ball end with an electrified body, charge is transferred to the curtain rod and the attached aluminium foil. Both the halves of the foil get similar charge and therefore repel each other. The divergence in the leaves depends on the amount of charge on them.
 Why material bodies acquire charge.?
We know that all matter is made up of atoms and/or molecules. Although normally the materials are electrically neutral, they do contain charges; but their charges are exactly balanced. Forces that hold the
molecules together, forces that hold atoms together in a solid, the adhesive force of glue, forces associated with surface tension, all are basically electrical in nature, arising from the forces between charged particles.
.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.
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. No new charge is created in the process of rubbing. Also the number of electrons, that are transferred, is a very small fraction of the total number of electrons in the material body. Also only the less tightly bound electrons in a material body can be transferred from it to another by rubbing.