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RESISTANCE AND OHM’S LAW

RESISTANCE AND OHM’S LAW. 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. Resistance .

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RESISTANCE AND OHM’S LAW

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

  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 (W) 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

  11. Finding Current • - cover the I • (V over R) divide • If V = 24 V and R = 8 W V

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

  13. 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

  14. 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

  15. 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

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

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