Electric Current Section 2

Current and Voltage Difference The net movement of electric charges in a single direction is an electric current Electric current is measure in amperes (A) One ampere is equal to 6,250 million billion electrons flowing past a point every second Electric charge will flow where there is a voltage difference Voltage difference is measured in volts

Electric Circuits A path that an electric current follows is a circuit A circuit path must be closed If a circuit path is broken, current will not flow What happens when you flip off a light switch? The circuit is broken

Batteries To keep electricity flowing, a voltage difference must be maintained A battery can supply that voltage difference Dry Cell Battery Consists of two electrodes surrounded by an electrolyte The electrolyte allows charge to move from one electrode to another In a dry cell the electrolyte is not a liquid

Batteries Wet Cell Batteries Lead-Acid Batteries Contain two connected plate made of different metals or metallic compounds in a conducting solution A wet cell batteries contains many wet cells connected together Lead-Acid Batteries Most car batteries Contains 6 wet cells Lead and Lead Dioxide plates Sulfuric Acid solution

Resistance When electrons flow through a material, the material will offer some resistance to the flow of electrons Resistance is due to collisions of the electrons with atoms in the material it is flowing through Some of the electrical energy of the electrons is converted to thermal energy Sometimes the resistance is great enough that it causes the material to glow Flashlight filaments Most materials offer some electrical resistance (except super conductors) Electrical conductors offer less resistance than electrical insulators

Resistance Temperature, Length, and Thickness will affect resistance Resistance tends to increase as temperature increases Resistance tends to increase as the distance traveled (length of the wire) increases Resistance tends to increase as the wire becomes thinner How could you manipulate a metal filament to become more resistant? Coil the metal to increase length Use thin wire Why would you want to? Filament must glow so resistance must be high

The Current in a Simple Circuit Simple circuit has A source of voltage difference battery A device that has resistance light bulb Conductors that connect the device to the battery terminals wires

Ohm’s Law Resistance, current, and voltage difference are related. The relationship is known as Ohm’s Law The current in a circuit equals the voltage difference divided by the resistance Current (in amps) = voltage difference (in volts) resistance (in ohms) I = V/R

Ohm’s Law Calculate the voltage difference in a circuit with a resistance of 25 ohms if the current is 0.5A 12.5 Volts

Ohm‘s Law A current of 0.5 A flows in a 60-W bulb when the voltage difference between the ends of the filament are 120 V. What is the resistance of the filament? 240 ohms