1. AND MR. SEREDA PRESENT….

2. Resisting the movement of Charge

4. Resistance EElectrons that travel through a light bulb Filament experience Resistance RResistance is a property that hinders motion AND converts electrical energy to other forms of energy E.g.: resistance of Tungsten wire is 400 times greater than copper When a current flow through the wire it is converted into ________________ and ________ Light Heat

5. Describing Resistance HHow much energy does it take to push a 50 kg crate across the floor? DDepends on resistance PPushing across a carpet would be harder than pushing across ice.

6. Resistance HHow much energy does it take to push a coulomb of charge across a filament? DDefined as the ratio of POTENTIAL DIFFERENCE across the LOAD PPOTENTIAL DIFFERENCE = VOLTAGE (V) LLOAD = CURRENT (I) V R = --- I Voltage Resistance = ------- Current

7. Units of Resistance UUnits of Resistance are called OHMS NNamed in honour of Georg Simon Ohm TThe symbol for Ohms is the greek letter OMEGA (Ω) OOhm was the first to publish results of various resistances on types of wires

8. Georg Ohm’s Findings OOhm took various types of conductors AApplied a current across the wire NNo matter what the Potential Difference (Voltage) --- the Resistance was the same CCalled Ohm’s Law

9. Ohm’s Law VV = IR VVoltage = Current x Resistance http://www.mhhe.com/physsci/physical/gia mbattista/circuits/circuits.html http://www.riedon.com/riedon_calculator.ht m

10. Model Problem WWhat is the resistance of the heating coil of an electric heater if a current of 12.5 A runs through it? II = 12.5 A VV = 120 V RR = V / I RR = 120 / 12.5 RR = 9.6 V / A RR = 9.6 Ω

11. Wasting Energy DDo resistors have to convert energy to a different source? CCan be used to control the current or Potential difference at different points in the circuit.

12. Measuring Resistance WWhat is the Resistance? RR = V / I VV = 6 II = 3 RR = 6 / 3 = 2 Ω 3 Amps Potential Difference = 6

13. Designing Circuit Materials FFour factors Affect Resistance LLength RResistance INCREASES with Length TThe longer the wire…the more resistance WWidth RResistance DECREASES with Width TThe wider the wire the less resistance TTemperature RResistance INCREASES with temperature TThe hotter the wire the more resistance MMaterial SSome material allows electrons to move more freely

14. CConducting wires that carry large currents have large diameters to minimize resistance. TThis is why stove cord is bigger than the cord for a kettle Copper Core Insulating Material

15. Do Questions 1 – 6 on Page 342 of the Textbook Worksheet: –http://www.kathimitchell.com/elect2.htmhttp://www.kathimitchell.com/elect2.htm