BMAT Physics Study Questions and Answers

Insulators charged by friction -when two insulators move relative to each other, friction between the two can result in both objects becoming electrically charged -one of the objects becomes positively charged and other is negatively -eg plastic being rubbed against duster -conductors can become charged but will only retain that charge of they are insulated from their surroundings. If not insulated, then any charge that builds up will leak away Charging by induction it's possible for objects to be charged by induction. Its like when an unmagnetised piece of iron becomes magnetised when placed near a magnet, a neutral object placed near to a charged object can become charged. If one end of an object charged by induction is momentarily earthed, allowing the charge that has accumulated at that end to leak away, then object becomes permanently charged. This is why uncharges objects (eg paper) can get attracted to charged objects (eg plastic) even though they are electrically neutral.// an uncharged object will become positively charged because electrons that were in it have been repelled to earth. Similarly, an object can become negatively charged by induction if electrons are attracted from earth Charging caused by gain or loss of electrons -atoms made up of protons and neutrons (bound together in the nucleus) and electrons (found on shells around nucleus). The electrons are the particles that form outer region of an atom. When an atom loses an electron, it has more protons than electrons, so positive charge. Atom gains electrons, negative charge. -when 2 objects rubbed together, friction causes the electrons transferring from one to the other, hence the 2 objects become electrostatistically charged. One becomes negatively charged, other is positively Conservation of charge the total charge remains the same. So for every object that becomes positively charges, another must become negatively charged. Which way the electrons move depends on which atoms attract the electrons more strongly. When 2 objects are rubbed together, electrons move away from the atoms that attract the, less strongly and towards the atom that attracts them more strongly. So whether a particular material becomes charged, when done so by friction, this depends on the nature of the 2 materials involved Like charges repel 2 charged objects placed near each other exert an electrostatic force on each other. The size of force depends on the size of the 2 charges and the distance between them. The larger the charges, the larger the force and the larger the distance of separation the smaller the force. Like charges repel, unlike charges attract