p.432-443

 Static Electricity – electrons stay in one place on the surface of objects  Current Electricity – continuous flow of electrons flow through a conductor in a controlled path

 Electrons are always moving  The steady flow of electrons in a circuit can be directed and used to power devices  Flow of electrons comes into wires and then into the device

 A continuous path in which electrons can flow  Analogy: circulatory system – a continuous path where blood travels through “wires” or blood vessels to where it is needed

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Conducting wire Switch Load Power source

 Also known as connecting wires  Join all parts of a circuit  Provides a path for electrons to flow  E.g. Copper, aluminum wires

 Controls current flow in an electric circuit  When the switch is “on” the circuit is CLOSED and the path is COMPLETE  When the switch is “off” the circuit is OPEN and the path is INCOMPLETE

 A device that transforms electrical energy into other usable forms of energy  Examples of loads: lamps, heaters, fans, computer hard drives, motor, iPOD

 Provides power for the electric device  There are small and large scale sources of energy  Example of small scale power source: batteries  Example of large scale power source: generating station

 A battery is a combination of electrochemical cells  An electrochemical cell is a package of chemicals that converts chemical energy into electrical energy that is stored in charged particles

 Portable device that converts chemical energy

into electrical energy

 Made up of two electrodes (conductors) in a conducting solution (electrolyte)  One electrode is positive,

the other negative

 In everyday language an electric cell is called a

battery

 In science, “battery” refers to two or more electric cells in combination  Electric cells are used in cameras, cell phones, flashlights

TYPE 1.WET CELL 2. DRY CELL Description

 2 metal electrodes are placed in a liquid (electrolyte) and react  Electrolyte conducts electricity  Continuously replace electrodes and electrolyte  The electrolyte is a paste  Electrons stop flowing as the negative electrode is used up

 Electric cells that cannot be recharged over and

over; can only be used once

 Examples: zinc chloride & alkaline

 Electric cells that can be recharged and reused many times; they are recycled  Examples: Lead-acid batteries (in cars) & nickel metal hydride batteries (NiMH), Lithium Ion used in cell phones

 Special type of battery through which a

continuous supply of chemicals is pumped as the cell operates

 A fuel cell can operate much longer than a typical electric cell.

 Is an electrochemical cell that generates electricity directly from a chemical reaction with fuel, such as hydrogen.

 Much of energy made is wasted as heat  Example: hydrogen fuel cell – produces electrical energy by converting hydrogen & oxygen into water.

 It is the difference in electric potential energy per unit of charge measured at two points  Also known as voltage

Potential and Electric

 The electric potential energy per unit charge is often abbreviated to: electric

potential

 Unit for voltage is volts (V)

 There is potential difference between two terminals of an electric cell.

 Electrons leave the negative terminal with electric potential energy that can be used to operate the motor

 As a result, the elections return to the positive terminal of a cell with less electric potential energy then they started because some of the energy was used to start the motor  Once inside the cell chemical reactions re-energize the electrons and send them out to the negative terminal again



In this way the electric cell acts like a pump

 A voltmeter is a device used to measure potential difference

 A voltmeter must be connected in parallel with a load or an energy source. The reason for this is because the energy is relative to two points.

Electric Current is the rate of electron flow past specific point in a circuit .



The unit for electric current is called the ampere (A). The symbol for current is I.



An ammeter is used to measure the current flow.

An ammeter must be connected in series to properly measure current flow in a circuit.

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Direct Current

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Alternating Current

 Electrons flow in one direction only  Is produced by an electric cell such as a battery to power portable electrical devices

    Electrons move back and forth, alternating their direction Is produced by generators at electric generating stations Used at electric generating stations because it is a more efficient method of distributing electrical energy over long distances than DC In an AC circuit, as the electrons move back and forth, there is an instant at which the electrons stop to change direction and at this point there is no electric current

Electrons move freely through the wire until they reach the light bulb's filament.

Chemical reactions within the battery cause electrons to be stripped away from the carbon electrode. Electrons will try to flow from a battery's negative terminal to its positive one, if allowed.

A loop of wire spinning through a magnetic field will create an alternating current. Note: current will flow only if the circuit connected to the generator is complete .

 Is the ability of a material to oppose the flow of electric current;

measured in ohms (Ω)



Symbol of Resistance: R



Symbol of Units of Resistance: Ω



Insulators

tend to minimize the amount of electron flow and it has a

high resistance



Conductors

have a very

low internal resistance

(this is why the electrons flow so easily in copper wires)

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Type of Material Cross-Sectional Area Length Temperature



The type of material within the material will affect how freely the electrons move



E.g. copper is an excellent conductor due to its low electrical resistance

 The diameter of the wire will indicate how well electrons flow 

The thicker the wire the less internal resistance and electrons have more room to move freely

 E.g. the greater the diameter of a water pipe, the greater the water flow

 The longer the wire, the greater the internal resistance and slow down because electrons have to travel through more material 

The longer the wire the warmer it gets

 E.g. dangerous for very long extension cords (to avoid overheating manufacturers make a larger-diameter wire)



When a wire gets warmer, the atoms in the wire gain energy and vibrate faster



More collisions ,

resistance increases with temperature



Ohmmeter – device used to measure resistance *ADD: OR can

calculate



When connecting an ohmmeter it must be

connected in parallel

with a load



Resistors are devices that are put into a circuit that reduce the flow of electric current so as to avoid overheating of the wire

 Some may consider any load a resistor but true resistors are specifically used for this purpose 

E.g. heavy ceramic resistors in larger circuits, lightweight carbon resistors in electronics OR dimmer switches and volume controls (called variable resistors

)

Read 11.1 and supplement your notes Complete p. 436 #1-3 p. 438 #1,3,4 p. 442 #1-3 p. 447 ?’s #2-5, 7-11