As shown in Figure 3, the negative and positive charges of the molecules are displaced slightly. A large charge nearby-not touching-will induce an opposite charge on the surface of the insulator. In contrast, charging by induction gives an object the charge opposite that of the charged rod.Įven though the charges are not free to travel throughout the material, insulators can be charged by induction. When an object is rubbed with a charged rod, the object shares the charge so that both have a charge of the same sign. This method of charging is called charging by induction (see Figure 2). If the hand is removed while the charged rod is still close, the electroscope will retain a charge. The electrons will be repulsed and flow out of the electroscope through the hand. Now, consider touching the electroscope knob with a finger while the charged rod is nearby. When the negative rod is removed, the leaves will fall. The leaves are left with a negative charge and therefore deflect. The electroscope is made of conducting material, so the positive charges are attracted to the knob by the nearby (but not touching) negatively charged rod. The electroscope will indicate the presence of charge but does not directly indicate whether the charge is positive or negative.Īn electroscope reports the presence of charge.Ī large charge near a neutral electroscope can make the leaves move apart. When a charged object touches the knob, the like charges repel and force the leaves apart. As shown in Figure 1, the electroscope consists of a conducting knob and attached lightweight conducting leaves-commonly made of gold foil or aluminum foil. An electroscope is a simple device used to indicate the existence of charge. An insulator is a material through which electric charges do not move easily, if at all. The net negative charge on the rod is equal to the net positive charge on the fur.Ī conductor is a material through which electric charges can easily flow. If the plastic rod and fur are initially neutral, when the rod becomes charged by the fur, a negative charge is transferred from the fur to the rod. Unlike charges attract each another that is, positive attracts negative.Like charges repel one another that is, positive repels positive and negative repels negative.The charge on plastic rubbed with fur is defined as negative, and the charge on glass rubbed with silk is defined as positive.Įlectrically charged objects have several important characteristics: A rod of plastic rubbed with fur or a rod of glass rubbed with silk will attract small pieces of paper and is said to be electrically charged. Electrostatics, as the name implies, is the study of stationary electric charges.
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