Resistance
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
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
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.
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)
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
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
Units Volts (V) Ohm’s (Ω) = Amperes (A) Resistance = Voltage/ Current
V = IR
Practice An electric toy has a resistance 120Ω and needs a current of 0.05A. How many 1.5V cells does it need?
V = (0.05A)(120Ω) = 6V Number of cells = 6V/1.5V cells = 4cells
Resistance increases as you add loads in series Resistance in Series Resistance increases as you add loads in series