ELECTRIC CurrentELECTRIC Current

Identify 3 sources of electric Identify 3 sources of electric currentcurrent Distinguish between current, Distinguish between current, voltage, & resistancevoltage, & resistance Ohm’s LawOhm’s Law How resistance changes in a How resistance changes in a wire wire

Info you Info you mustmust knowknow

You remember that Static Electricity is where electrons have gathered and are not moving.

Give these electrons a wire to travel in and they become

known as Electric Current.

Sources of ELECTRIC Sources of ELECTRIC CURRENTCURRENT

Electrochemical Cells - Electricity can be gene-rated by chemical reactions within an enclosedcontainer commonly called a battery.

Two types of BatteriesTwo types of Batteries

Wet cell an automobile battery is an exampleof a wet cell. A wet cell contains lead and lead oxide plates called electrodes and a liquid con-ductor called an electrolyte. (usually H2SO4,

sulfuric acid)

SOURCES SOURCES (CONTINUED)(CONTINUED)

-- - - - - - - - - -

- - - - - - - - - -

Lead plate

Liquid electrolyteH2SO4 (sulfuric acid)

The chemical reactionbetween the acid and the lead plates releaseselectrons to be used aselectrical current.

+ pole - pole

Wet Cell Battery

SOURCES SOURCES (CONTINUED)(CONTINUED)

Dry cell batteries work in much the same way as wet cells except that the electrodes in a dry cellare made of zinc and carbon. The electrolyte is usually a dry or semi-moist chemical such as ammonium chloride.

Dry cells come in varying sizes and are usedin things like flashlights, radios, remote controls,toys, etc.

SOURCES SOURCES (continued)(continued)

Thermocouples

A thermocouple is a device capable of generatingelectric current due to a difference in temperatures.

This simple device consists of an iron wire and acopper wire with the ends joined together to form a loop.

Electric current is produced when one iron/copperjunction is heated and the other is cooled.

The The THERMOCOUPLETHERMOCOUPLE

Copper wire

Iron wire

Junctionbeing heated Junction

being cooled

Ammeter Device which detectselectrical current

SOURCES SOURCES (CONTINUED)(CONTINUED)

Thermocouples are used in things like:

1. Automobile temperature gauges

2. Safety device (switch) in furnaces or ovens.

TYPES OF CURRENTTYPES OF CURRENT

There are two types of current.

Direct Current (DC) is electrical current which comes from a source which delivers a steady flow of electrons such as an electro-chemical cell (battery) Alternating Current (AC) is when the elec- trons in the current change directions. This direction change occurs about 120 times per second. The current in your home is (AC).

MEASURING CURRENTMEASURING CURRENT

Flow rate The rate at which electricity flowsthrough a wire can be compared to waterflowing through a hose.

A small diameter wire allows less flow

A larger wire allows more flow.

This can be compared to water flowing through agarden hose and a fire hose.

How is Flow Rate How is Flow Rate measured?measured?

The number of electrons that pass a given point in acircuit in one second indicates the flow rate of electriccurrent.

The > the number of electrons the > the current.

Symbol for current is a capital I

Current is measured with an instrument called anAMMETER

The unit of measurement is called the ampere(amps) symbol is a capital A

MEASURING CURRENT MEASURING CURRENT (CONTINUED)(CONTINUED)

VOLTAGE

Voltage is the amount of energy available to moveelectrons through a wire.

The > the voltage the > the ability of the electrons todo work. (i.e. the brighter the light in the flashlight)Voltage is measured with an instrument called avoltmeter.The symbol for voltage is the capital letter V

VOLTAGEVOLTAGE

In order to keep electrons flowing through a wirethere must be a source of electrons. This source must also provide a difference in in the charges present at each end of the wire. One end of the wire must be + positively charged and the other endmust be - negatively charged. The difference inthe charges at each end of the wire is called POTENTIAL DIFFERENCE or VOLTAGE .

RESISTANCERESISTANCE

RESISTANCE

The best way to show resistance is to talk about the

Electricity flowsfreely through thecopper wire leadingto the light bulb

Once the current gets tothe smaller wire filament in the bulb it slows downbecause of the resistanceof tungsten metal to theflow of electricity.

When the resistance slows the flow down a glow is producedin the wire as the electrons pass through it.

RESISTANCE RESISTANCE (CONTINUED)(CONTINUED)

The symbol for resistance is the capital letter R.

The unit for resistance is the ohm .

The symbol for the ohm is the Greek letter “omega:

Ohm’s LawOhm’s Law

Ohm’s Law states the current in a circuit is equal to the voltage divided by the resistance.

I = VR

I - CurrentV - VoltageR - Resistance

V

I R

Using Ohm’s LawUsing Ohm’s Law

1. The electric current in a hair dryer measures10 amps. The resistance is 12 ohms. What is thevoltage?

V = I x R

V = 10 A x 12 ohms

V = 120 V

Ohm’s Law Ohm’s Law AGAINAGAIN

2. Two dry cells in a flashlight produce 3 V .The dry cells carry a current (I) of 0.5 A.What is the resistance of the flashlight?

R = V I

R = 3V 0.5 A

R = 6 ohms

ONE LAST ONE LAST OHM’S LAWOHM’S LAW

3. What is the current if 120 V passes through aradio with a resistance of 1800 ohms?

I = V R

I = 120 V 1800 ohms

I = .066 A (amps)

Quiz1.Electrons moving along a wire are called____________ __________.2.The two main components of electro-

chemical cells are ________ & ______.3.A device that generates electrical current

because of a difference in temperature isa __________________.

4.Electrochemical cells deliver _________current.

5.The current used in homes is _________current.

6.Current is measured with a device calleda _______________.

7. The symbol for current is ________.

Quiz continued8.The unit for current is the__________.9.The amount of energy available to move

electrons is called ______________.10.The difference in charges at each end

of a wire is called ________ ________.11. _________ is those “things” that elec-

tricity causes to work.12.The Ohm’s Law formula is __________.

THE ANSWERS1.ELECTRIC CURRENT2.ELECTRODES & ELECTROLYTES3.THERMOCOUPLE4.DIRECT5.ALTERNATING6.AMMETER7.I8.AMPERE9.VOLTAGE10.POTENTIAL11.RESISTANCE12.I = V / R

8 PTS FOR EACH X

The end !!