1. Resistance in Circuits

2. What is it?
Resistance is the ability to impede (oppose) the flow of electrons

3. What is the effect of resistance?
When electrons flow through a load, or a conductor, resistance causes a loss in voltage
There is now a difference in the amount of voltage after the electron has flowed through the load

4. Short form: R
Unit: Ohm (Ω)
Circuit Symbol:

5. Resistance is measured with an ohmmeter in parallel with the load

6. Factors affecting resistance
Type of material: some materials conduct better than others
Cross-sectional area: as area increases, resistance decreases
Length of wire: as length increases, resistance increases
Temperature: as temperature increases, resistance increases
Resistor: type of load

7. Relating Current, Voltage, and Resistance – Ohm’s Law
As the potential difference across a load increases, so does the current.
As the resistance increases current decreases

8. Ohm’s Law
V = I x R
R = V ÷ I
I = V ÷ R V I R

9. An Example:
If you have a 6V battery and a 1.5 Ω light bulb, what will the current be?
G: V = R = 1.5
R: I = ?
A: I = V ÷ R
S: I = 6V ÷ 1.5 Ω
= 4 A
S: The current through the light bulb will be 4 amps. V I R

10. Ohm-my goodness – homework!
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Worksheet