1. RESISTANCE AND OHM’S LAW

2. A closer look at insulators and conductors Conductors: electrons loosely bound to nuclei –Electrons flow easily when voltage is applied –Eg: most metals Insulators: electrons tightly bound to nucleus –Electrons do not flow easily –Eg: glass and rubber

3. Resistance A measure of how difficult it is for current to flow through a material (Resists or slows down charges, which reduces current) Depends on material, thickness, length and temperature The lower the resistance, the better the conductor

4. Examples of Resistors Light bulb filament (thin wire that glows) Heating elements on stove or in oven Heating wires inside a toaster Resistors convert electrical energy to heat or light

5. Rheostats Variable resistors Used to adjust the amount of current flowing Examples: temperature control on stove dimmer switch volume control knob

6. Calculating Resistance Resistance can be calculated from voltage and current Mathematical relationship is called Ohm’s Law (after Georg Simon Ohm)

7. OHM’S LAW Resistance is measured in Ohms (  NOTE: Must use these base units, not milliAmps, kiloVolts etc.

8. 3 Forms of Ohm’s Law

9. Memory Aids for Ohm’s Law V

10. Finding Resistance - cover up R (V over I) - divide If V = 12 Volts And I = 2 Amps V

12. - cover the I (V over R) divide If V = 24 V and R = 8  V Finding Current

14. Finding Voltage - cover the V (I beside R) multiply If I = 500 mA = 0.5 A and R = 20 

17. Examples A small portable stove operates from a 120V outlet. When it is in use, 6A flow through it. What is the resistance of the heating element on the stove? R= V/I = 120V/6A = 20 Ω

18. The filament of a certain light bulb has a resistance of 96 Ω. To operate at its proper brightness, it needs a current of 1.25A to pass through it. What voltage must be applied to this light bulb to make it work? V = I R = 1.25 A x 96 Ω = 120V

19. If a kettle is operated from a 120V outlet and its heating element has a resistance of 10 Ω, what current is in the heating element? I = V / R = 120V / 10 Ω = 12 A

20. Ohm’s Law Worksheet For each question: (example) Show formula V = I x R Show work = 2 A x 6  Include correct units = 12 V