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Unformatted text preview: Electrostatic Force An electromagnetic force exists between two objects provided both bodies have an electrical charge. In a neutral ground-state atom, the electromagnetic forces exerted by the negatively-charged electrons on some external charged body are canceled by the forces exerted by the equal number of positively-charged protons on that object. The negative electrons furthest from the attractive force of the atoms positive proton-bearing nucleus are capable of being removed from one atom and added to another. Like-charged particles will repel each other whereas oppositely-charged particles attract one another. A net negative charge is due to an excess of electrons while a net positive charge is due to a loss of electrons relative to the number of protons present in the object. The Electroscope The detection of electromagnetic forces requires either the addition or removal of negative electrons. If both bodies contain an excess of electrons (negatively-charged) or an excess of protons (positively-charged) a repulsive electric force exists between the objects. Electrons from atoms of fur or wool tend to migrate to rubber, giving the material a net negative charge. Glass tends to transfer electrons from its atoms to silk, giving the glass a net positive charge. An electroscope consists of a metal rod to which is attached a free-moving conductor or leaf. The rod passes through an insulator into a metal enclosure which surrounds the leaf. An object (rod) is typically touched to (conductive-charging) or held nearby (inductive-charging) the knob causing the movement of electrons into leaves or from the leaves to the knob. An excess or deficiency of electrons in the leaves will result in a repulsive effect between like charges causing the leaves/needle to repel each other. Note that the movement of the leaves does not indicate the type of charge on the electroscope. Charging by conduction occurs whenever a body acquires a net charge of equal magnitude and sign as the charging body. To charge an electroscope by conduction , a positively or negatively charged object makes physical contact with the knob of the electroscope. If a positively-charged glass rod is placed nearby the scope, negative electrons are drawn from the electroscope leaves to the knob. As the electrons from the knob and leaves of the electroscope are transferred into the rod, the entire scope is left with a net positive charge. Charging by conduction means that the charging body contacts the electroscopes knob. With an ebonite rod rubbed with fur, electrons transfer from the negative rod to the knob resulting in a net negatively-charged scope. Electroscope charged by conduction where electrons are transferred from the leaves/knob of the to a positively-charged glass rod....
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