Electrical Resistance Electrons like any other moving body follow the path of least resistance. Truemper 10/24/2011
Which road would you rather travel on?
Resistance “Electrical Friction” Opposition to the flow of moving electrical charges Truemper 10/24/2011
Symbol for Resistance R Truemper 10/24/2011
Unit of Measurement ohm Truemper 10/24/2011
“Resistance is Futile”? If resistance is “electrical friction”, what benefits could resistance provide when making a circuit? Truemper 10/24/2011
Is resistance futile in a lightbulb? Truemper 10/24/2011
What kind of wires would increase resistance in a circuit? Truemper 10/24/2011
Resistance slows down moving electrons Resistance slows down moving electrons. When electrons slow down they convert electrical energy into light, heat and sound What impacts resistance in a wire? Truemper 10/24/2011
4 things that can change resistance
The resistance in a wire depends on: A metals structural resistance to electron flow Truemper 10/24/2011
The resistance in a wire depends on: 1. The type of metal in the wire Which metals have low resistance? Which metals have high resistance? Truemper 10/24/2011
The resistance in a wire depends on: 1. The type of metal in the wire Which metals have low resistance? Silver and Copper Which metals have high resistance? Nichrome and Tungsten Truemper 10/24/2011
The resistance in a wire depends on: Length of the wire The shorter the wire the less resistance there is Truemper 10/24/2011
The resistance in a wire depends on: Thickness (Cross Sectional Area) of the wire The wider the wire the less resistance there is Truemper 10/24/2011
The resistance in a wire depends on: Temperature: The colder it is the less resistance there is Truemper 10/24/2011
Is resistance in a wire always bad? Problem of the Day Is resistance in a wire always bad? bulbResistance.mp4 Truemper 10/24/2011
Is resistance in a wire always bad? Problem of the Day Is resistance in a wire always bad? Without resistance, there would be no light Resistance allows electrical energy to change forms into light, heat or sound Truemper 10/24/2011
How different types of light bulbs work Problem of the Day How different types of light bulbs work Truemper 10/24/2011
Why are different wires used with different appliances? Problem of the Day Why are different wires used with different appliances? Scroll down on webpage to speaker scence http://www.stmary.ws/highschool/physics/home/notes/electricity/circuits/ResistanceWire.htm Truemper 10/24/2011
Truemper 10/24/2011
Ohm’s Law V= I x R Voltage (Volts)= Current (Amps) times Resistance (ohms) electric current is directly proportional to voltage and inversely proportional to resistance Truemper 10/24/2011
Ohm’s Law Practice Problem How much current is in a circuit with a 9 V battery and a light bulb with a resistance of 3 ohms? Current (A) Voltage (V) Resistance (Ω ) Formula Answer with Unit Looking for this I= ? 9V 3Ω I = (V/R) V divided by R Truemper 10/24/2011
Ohm’s Law Practice Problem How much current is in a circuit with a 9 V battery and a light bulb with a resistance of 3 ohms? Current (A) Voltage (V) Resistance (Ω ) Formula Answer with Unit Looking for this I= ? 9V 3Ω I = (V/R) V divided by R 3A Truemper 10/24/2011
Ohm’s Law Practice Problem What is the voltage of a circuit with 15 A of current and a toaster with 8 ohms of resistance? Current (A) Voltage (V) Resistance (Ω ) Formula Answer with Unit 15 A V= ? 8 V= I R Truemper 10/24/2011
Ohm’s Law Practice Problem What is the voltage of a circuit with 15 A of current and a toaster with 8 ohms of resistance? Current (A) Voltage (V) Resistance (Ω ) Formula Answer with Unit 15 A V= ? 3 V= I R 45 V Truemper 10/24/2011