1. Resistance

2. 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

3. 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

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

5. Calculate the resistance? 3A
12V

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

7. 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

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

11. 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)

12. Temperature
As temperature increases, resistance increases.