1. Resistance

2. Electrical Resistance
The property of a substance that slows electric current and converts electrical energy to other forms of energy
Resistor: a device used to decrease the current by a specific amount

3. Resistor
A resistor can be made to slow current by a certain amount or a resistor can be a load that changes energy to do work

4. Loads
A resistor that transforms electrical energy to heat, (kinetic) motion, sound or light energy
We harness the released energy in the form of light bulbs, electric heaters, toasters etc.

5. Factors affecting
Resistance is caused by electrons bouncing off atoms and ions of the conductor The more the electrons bounce the more resistance there is…. (particle theory +heat)

6. Factors Affecting Resistance
Material: Conductors have less resistance than insulators
Temperature: higher temperatures increase resistance
Cross-section: larger cross section has less resistance
Length: Longer wires have more resistance
# of loads increases resistance

7. Ohm’s law
Found that there was a constant relationship between the ratio of potential difference (V) and current (I)
That constant is known as resistance
As resistance increases, current decreases if voltage stays the same

8. Units
Volts (V)
Ohm’s (Ω) =
Amperes (A)
Resistance = Voltage/ Current

9. V = IR

10. Practice
An electric toy has a resistance 120Ω and needs a current of 0.05A. How many 1.5V cells does it need?

11. V = (0.05A)(120Ω)
= 6V
Number of cells = 6V/1.5V cells
= 4cells

12. Resistance increases as you add loads in series
Resistance in Series
Resistance increases as you add loads in series