Electric Charge Electricity Objects can be described by

Electric Charge

Electricity ] Objects can be described by fundamental properties. • Mass, velocity, energy, temperature, volume, etc. ] In ancient times is was observed that some items attracted small bits of material, especially when rubbed. ] Fossilized tree sap called amber had this property. • Greek word for amber is elektron ] The property was called electricity.

Static Electricity ] A person walking on a carpet picks up a negative charge. It follows that something else • • A) becomes equally negatively charged. B) becomes equally positively charged. C) becomes charged, but the amount depends on the material. D) becomes magnetized.

Charge ] Electric charge is measured in coulombs (C). ] Electric charges come in small, but discrete units. • Electron charge is 1. 6 x 10 -19 C • Proton charge equal magnitude to the electron charge ] Charges come in two types – positive and negative. • Electron is negative, proton is positive ] The sum of all charges is conserved.

Positive and Negative ] Rubbing a silk cloth on a glass rod charge both the cloth and rod. • Extra electrons on cloth ] The combination is still electrically neutral.

Attract or Repel ] Two objects with opposite sign charge will attract. + - ] Two objects with the same sign charge will repel. + +

Polarized ] Positive and negative charges may not be uniform in an object. ] Charges can orient themselves to attract to another charge. ] This is called polarization. • Allows neutral items to be attracted.

Charge Transfer ] Many items will transfer charge when they rub together. ] If one item gains positive charge, another item loses an equal amount to become negatively charged. ] Different items are more likely to gain positive or negative charge. ] Contact sequence from most positive to most negative: • • • Rabbit Fur Glass Wool Silk Human Skin Cotton Wood Amber Rubber next