Electric Forces and Fields Electric Charge

Electric charge – an electrical property of matter that creates a force between objects Experience movement of electric charge as shock

Electric Charge Two types of charges –Positive and negative –Like charges repel –Opposite charges attract If positive and negative charges are equal, an object has no net charge

Electric Charge Electric charge depends on the imbalance of protons and electrons –Protons are positive –Neutrons are neutral –Electrons are negative Total electric charge is conserved –For every positive charge there exists a negative charge

Electric Charge Negatively charged objects have more electrons than protons Positively charged objects have more protons than electrons Unit for electric charge is the coulomb (C) Electrons and protons have the same amount of charge: * C or ±e –Protons have a charge of * C or +e –Electrons have a charge of * C or –e Charge of an electron was measured by Robert Millikan

Electric Charge Conductor – a material that transfers charges easily –Example: metals Insulator – a material that does not transfer charge easily –Examples: plastics, cardboard, glass, silk Semiconductors – somewhere in between a conductor and an insulator Superconductor – certain materials become perfect conductors below a certain temperature

Electric Charge Four methods to charge an object Objects are charged by the transfer of electrons –Charging by friction – two neutral objects rub together –One object gains electrons – becomes negative –One object looses electrons – becomes positive

Electric Charge

Charging by contact – touching a neutral object with a charged object –Neutral object takes the same charge as the charged object –Charged object remains charged, but with a smaller charge

Electric Charge

Induction – the process of charging a conductor by bringing it near another charged object and grounding the conductor –Grounding – connecting on object to the Earth using a conducting wire The Earth is an infinite reservoir of electrons –It can accept or supply an infinite supply of electrons Induced charges – bringing a charged object near a neutral object causes the neutral object to become polarized –The part of the object near the charged object has a charge opposite the charged object –The part of the object away from the charged object has the same charge as the charged object

Electric Charge

Surface charges can be induced on insulators by polarization –The positive and negative centers of charge on a neutral object shift to opposite sides of a neutral molecule