Resistance.

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Presentation transcript:

Resistance

Resistance Resistance is anything in a circuit that restricts the flow of current It can be calculated using Ohm’s Law: V I x R Resistance = Voltage (V) (Ohms) Current (A) The unit of Resistance is the Ohm

Ohm's Law V = I R Voltage In volts (joules / coul) Current In amperes (coul / second) Resistance In ohms (volts / amp) Drop across a resistance Current passing through the resistor

Sample Problem How much current is in a circuit that includes a 9volt battery and a bulb with a resistance of 3 ohms?

Calculate the resistance ? 3A 12V

Factors Affecting Resistance Thickness (diameter) of wire Length of wire Type of material Temperature

Cross Sectional Area -Thin wires have more resistance than thick wires -Halving (1/2) the cross sectional area of a wire doubles its resistance because there is half as much space for the electrons to move

Resistance - Length of Wire -Doubling the Length of a wire doubles its resistance because the electrons have twice as far to move

Type of Material Different materials have different resistances. Example: A nichrome wire (alloy) has more resistance than a copper wire of the same size (the atoms in nichrome hold the electrons more tightly than copper atoms)

Temperature As temperature increases, resistance increases.