Electric CurrentSECTION 2

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

Current and Voltage Difference

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

Electric Circuits

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 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

Batteries

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

Resistance

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

The Current in a Simple Circuit

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

Ohm‘s Law