9.1 STATIC ELECTRICITY Electricity involves the movement of electrons Electrons are incredibly small, have almost no mass, have a charge of –1 and can be removed from atoms quite easily There are two different types of electricity 1. STATIC – a charge that stays on an object and does not move, unless it comes into contact with another object 2. CURRENT – a charge that flows from one place to another (i.e. around a circuit) 2 types of charge: 1. POSITIVE – results from a net LOSS of electrons 2. NEGATIVE – results from a net GAIN of electrons Do neutral objects have charges? Can neutral objects become charged? YES – the negative and positive charges on a neutral object are EQUAL to one another ( the charges are BALANCED) YES! – rubbing two neutral objects together (called CHARGING BY FRICTION) causes the movement of electrons One object will lose electrons and will therefore become positively charged The other object will gain electrons and will therefore become negatively charged How can we tell which object becomes positive and which one becomes negative (without doing an experiment!)? Use the ELECTROSTATIC SERIES (a list of common objects describing how ell they hold on to their electrons) Weak hold on electrons ( become positive when rubbed) acetate glass wool cat’s fur/human hair calcium/magnesium/lead silk aluminum/zinc paraffin wax Strong hold on electrons (become negative when rubbed) ebonite polyethylene (plastic) carbon/copper/nickel rubber sulfur platinum/gold When 2 substances are rubbed together, the one HIGHER in the series always LOSES electrons (and becomes positively charged) while the one LOWER in the series always GAINS electrons (and becomes negatively charged) LAW OF ATTRACTION AND REPULSION LIKE charges always REPEL OPPOSITE charges always ATTRACT NEUTRAL objects are ATTRACTED by CHARGED objects Why does a charged object attract a neutral object? I.e. if all of the charges in a neutral object are balanced, why then does the charged object attract it? Does the neutral object gain or lose charge? NO!!! – the charged object pulls the opposite charges in the neutral object so that the charges in the object are rearranged Neutral piece of paper Positively charged glass rod When the two objects are brought close together, the charges in the paper rearrange themselves so that most of the negative charges move closer to the positive charges in the rod. This creates a more negative charge on the side of the paper closest to the glass rod, which allows the two objects to be attracted to one another Force of attraction between the two objects