Electrical Resistance

Electrons like any other moving body follow the path of least resistance.

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Resistance

“Electrical Friction”

Opposition to the flow of moving electrical charges

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“Resistance is Futile”?

If resistance is “electrical friction”, what benefits could resistance provide when making a circuit?

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Is resistance futile in a lightbulb?

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Symbol for Resistance

R

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Unit of Measurement

ohm

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What kind of wires would increase resistance in a circuit?

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Resistance slows down moving electrons.

When electrons slow down they convert electrical energy into light, heat and sound

What impacts resistance in a wire?

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4 things that can change resistance

The resistance in a wire depends on:

A metals structural resistance to electron flow

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The resistance in a wire depends on:

1. The type of metal in the wire

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Which metals have low resistance?

Which metals have high resistance?

The resistance in a wire depends on: 1. The type of metal in the wire

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Which metals have low resistance?

Silver and Copper

Which metals have high resistance?

Nichrome and Tungsten

The resistance in a wire depends on:

Length of the wireThe shorter the wire the less resistance there is

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The resistance in a wire depends on:

Thickness (Cross Sectional Area) of the wireThe wider the wire the less resistance there is

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The resistance in a wire depends on:

Temperature:The colder it is the less resistance there is

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Problem of the Day

Is resistance in a wire always bad?

bulbResistance.mp4

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Problem of the Day

Why are different wires used with different appliances?

Scroll down to the speaker playing music

http://www.stmary.ws/highschool/physics/home/notes/electricity/circuits/ResistanceWire.htm

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Ohm’s LawV= I x RVoltage (Volts)=Current (Amps) times Resistance (ohms)

electric current is directly proportional to voltage and inversely proportional to

resistance

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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?

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Current (A) Voltage (V) Resistance (Ω )

Formula Answer with Unit

Looking for thisI= ?

9V 3Ω I = (V/R)V divided by R

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?

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Current (A) Voltage (V) Resistance (Ω )

Formula Answer with Unit

Looking for thisI= ?

9V 3Ω I = (V/R)V divided by R

3A

Ohm’s Law Practice Problem

What is the voltage of a circuit with 15 A of current and a toaster with 10 ohms of resistance?

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Current (A) Voltage (V) Resistance (Ω )

Formula Answer with Unit

15 A V= ? 10 V= I R 150 V

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?

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Current (A) Voltage (V) Resistance (Ω )

Formula Answer with Unit

15 A V= ? 8 V= I R 15 A

OHM’s Law Summary

If Voltage increases, Current _____________

If Resistance increases, Current ____________

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Ohm’s Law Summary

If Voltage increases, Current increasesMore batteries = More current

If Resistance increases, Current decreasesMore load = lower current

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Question of the Day

• What 4 things affect a circuit to give it more/less resistance?

Answer

1) Type of conductor used2) Length of wire3) Width of wire4) Temperature