Charging an object by induction Electrostatic induction

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gold-leaf electroscope, showing induction, before terminal grounded.


however, induction effect can used put net charge on object. if, while close positive charge, above object momentarily connected through conductive path electrical ground, large reservoir of both positive , negative charges, of negative charges in ground flow object, under attraction of nearby positive charge. when contact ground broken, object left net negative charge.


this method can demonstrated using gold-leaf electroscope, instrument detecting electric charge. electroscope first discharged, , charged object brought close instrument s top terminal. induction causes separation of charges inside electroscope s metal rod, top terminal gains net charge of opposite polarity of object, while gold leaves gain charge of same polarity. since both leaves have same charge, repel each other , spread apart. electroscope has not acquired net charge: charge within has merely been redistributed, if charged object moved away electroscope leaves come again.


but if electrical contact briefly made between electroscope terminal , ground, example touching terminal finger, causes charge flow ground terminal, attracted charge on object close terminal. charge neutralizes charge in gold leaves, leaves come again. electroscope contains net charge opposite in polarity of charged object. when electrical contact earth broken, e.g. lifting finger, charge has flowed electroscope cannot escape, , instrument retains net charge. charge held in top of electroscope terminal attraction of inducing charge. when inducing charge moved away, charge released , spreads throughout electroscope terminal leaves, gold leaves move apart again.


the sign of charge left on electroscope after grounding opposite in sign external inducing charge. 2 rules of induction are:



if object not grounded, nearby charge induce equal , opposite charges in object.
if part of object momentarily grounded while inducing charge near, charge opposite in polarity inducing charge attracted ground object, , left charge opposite inducing charge.




^ cope, thomas a. darlington. physics. library of alexandria. isbn 1465543724. 
^ hadley, harry edwin (1899). magnetism & electricity beginners. macmillan & company. p. 182. 






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