12 Gustav Kirchhoff 1824 – 1887 Invented spectroscopy with Robert Bunsen Formulated rules about radiationFormulated the Kirchhoff’s rules
13 Kirchhoff’s RulesWhy do you need kirchhoff’s rules?
14 Statement of Kirchhoff’s Rules Junction RuleThe sum of the currents entering any junction must equal the sum of the currents leaving that junctionA statement of Conservation of ChargeLoop RuleThe sum of the potential differences across all the elements around any closed circuit loop must be zeroA statement of Conservation of Energy
16 Setting Up Kirchhoff’s Rules Assign symbols and directions to the currents in all branches of the circuitIf a direction is chosen incorrectly, the resulting answer will be negative, but the magnitude will be correctWhen applying the loop rule, choose a direction for transversing the loopRecord voltage drops and rises as they occur
23 Electrical Safety Electric shock can result in fatal burns Electric shock can cause the muscles of vital organs (such as the heart) to malfunctionThe degree of damage depends onthe magnitude of the currentthe length of time it actsthe part of the body through which it passes
24 Effects of Various Currents 5 mA or lessCan cause a sensation of shockGenerally little or no damage10 mAHand muscles contractMay be unable to let go a of live wire100 mAIf passes through the body for just a few seconds, can be fatal
25 Ground WireElectrical equipment manufacturers use electrical cords that have a third wire, called a case groundPrevents shocks
26 Ground Fault Interrupts (GFI) Special power outletsUsed in hazardous areasDesigned to protect people from electrical shockSenses currents (of about 5 mA or greater) leaking to groundShuts off the current when above this level