Current ElectricityCurrent Electricity

Let’s review what we know about Let’s review what we know about electric charges:electric charges:

Objects are made of negative and Objects are made of negative and positive chargespositive charges

Like charges repel and opposite Like charges repel and opposite charges attractcharges attract

Negative charges (electrons) are free Negative charges (electrons) are free to move from atom to atomto move from atom to atom

Positive charges (protons) cannot Positive charges (protons) cannot movemove

Current ElectricityCurrent Electricity Until now, we have only been looking at Until now, we have only been looking at

charges that were static (not moving on an charges that were static (not moving on an object). object).

If these charges are allowed to move in a If these charges are allowed to move in a controlled way, (say in a conductor) it is controlled way, (say in a conductor) it is now called current electricity. now called current electricity.

In current electricity, large groups of In current electricity, large groups of electrons continuously move around a electrons continuously move around a path. path.

Each electron is forced through the path Each electron is forced through the path by charges elsewhere in the circuit.by charges elsewhere in the circuit.

In all cases of current electricity, In all cases of current electricity, energy is required to move the energy is required to move the charges around the path (called a charges around the path (called a circuit). circuit).

A cell phone uses a battery; a A cell phone uses a battery; a calculator uses a solar cell; a lamp calculator uses a solar cell; a lamp uses the wall plug. uses the wall plug.

Types of CurrentTypes of Current

Current electricity comes in two Current electricity comes in two different types: different types: • Direct Current (DC)Direct Current (DC)• Alternating Current (AC)Alternating Current (AC)

DC CurrentDC Current In DC, the electrons flow In DC, the electrons flow

around the circuit in one around the circuit in one direction, from the direction, from the negative end to the negative end to the positive end. positive end.

Electrons flow negative to Electrons flow negative to positive because they are positive because they are negatively charged.negatively charged.

Electrons are attracted to Electrons are attracted to the positive end of the the positive end of the battery and repelled from battery and repelled from the negative end.the negative end.

All batteries produce DC All batteries produce DC electricity. electricity.

Electrochemical CellsElectrochemical Cells Often mis-called ‘batteries’Often mis-called ‘batteries’ Converts chemical energy to Converts chemical energy to

electrical energyelectrical energy Made up of two electrodes Made up of two electrodes

(conductors made of (conductors made of different materials) in an different materials) in an electrolyte (a conduction electrolyte (a conduction solution)solution)

A chemical reaction occurs A chemical reaction occurs with the materials to with the materials to negatively charge one negatively charge one electrode and positively electrode and positively charge the othercharge the other

So What Is a Battery?So What Is a Battery? A Battery is more than A Battery is more than

one cell connected one cell connected togethertogether

A battery can provide A battery can provide more energy than a more energy than a single cellsingle cell

Connecting them in Connecting them in different orientations different orientations gives you different gives you different amounts of energy for amounts of energy for different amounts of different amounts of timetime

Primary vs Secondary CellsPrimary vs Secondary Cells

There are two main types of cells:There are two main types of cells:• PrimaryPrimary

Chemical reactions are not reversibleChemical reactions are not reversible Once all of the chemicals are used up, they are Once all of the chemicals are used up, they are

uselessuseless

• SecondarySecondary Chemical reactions are reversibleChemical reactions are reversible Once the chemicals are used up, electricity (from a Once the chemicals are used up, electricity (from a

charger) can be used to reverse the chemical charger) can be used to reverse the chemical reactionreaction

There is a limit to how many times they can be There is a limit to how many times they can be charged and dischargedcharged and discharged

Fuel CellFuel Cell A fuel cell works much A fuel cell works much

like a regular like a regular electrochemical cellelectrochemical cell

The main difference is The main difference is that the waste that the waste chemicals are chemicals are constantly removed constantly removed from the reaction so from the reaction so that only the desired that only the desired chemicals are presentchemicals are present

Fuel cells can last Fuel cells can last much longer than much longer than conventional cellsconventional cells

AC SourcesAC Sources

AC GeneratorsAC Generators All AC generators work on the same All AC generators work on the same

principleprinciple They convert mechanical energy (motion) They convert mechanical energy (motion)

into electrical energyinto electrical energy A coil of wire is spun in between two A coil of wire is spun in between two

powerful magnetspowerful magnets Due to ‘electromagnetic induction’, Due to ‘electromagnetic induction’,

electricity is produced in the coilelectricity is produced in the coil

Ways to spin the coil…Ways to spin the coil… All generators need ways to spin the All generators need ways to spin the

coil of wirecoil of wire• Hydroelectricity uses falling waterHydroelectricity uses falling water• Wind turbines use windWind turbines use wind• Nuclear plants use steam to turn Nuclear plants use steam to turn

turbinesturbines

How does AC work?How does AC work?

http://www.youtube.com/watch?v=hPhttp://www.youtube.com/watch?v=hP1r7sRVgas&feature=fvwrel1r7sRVgas&feature=fvwrel

HomeworkHomework

Read p432-6Read p432-6 Answer Questions 1-5 on p 436Answer Questions 1-5 on p 436 Read p437-8Read p437-8 Answer Questions 1-5 on p 438Answer Questions 1-5 on p 438