Unit 6 Current Electricity and Circuits

2 Types of Electricity Electrostatics –Electricity that is not in motion. Current Electricity –Electricity that is in motion. –Occurs whenever an electric charge moves through a conductor.

2 Types of Current Electricity Direct Current (DC) –Electricity that ONLY flows in one direction. –Typical in circuits operating with cells (batteries) Alternating Current (AC) –Electricity that moves back and forth at regular intervals. –Typically found in household outlets. –In North America we have 110 V operating at 60 Hz –In Europe they have 220 V operating at 50 Hz.

Definition of Electric Current Electric Current is the amount of electrons (or charge) that flows through a cross sectional area of a conductor per a certain period of time. e-e- UNITS?? Amperes

Example: Find the amount of current in a wire that has 10.0 C of charge passing through every 2.0 seconds.

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Direction of Direct Current Consider a simple circuit Conventional Flow: Electricity was thought to have traveled from the abundance of electricity (positive) to the deficiency of electricity (negative) This was thanks to Ben Franklin

Unfortunately Ben got it wrong. It is actually electrons that flow in a circuit. Electron Flow: Electrons travel away from the negative of a cell, through the circuit, and are attracted towards the positive of the cell. However many university still use conventional flow when talking about the direction electricity flows Page 594 #4

Electric Potential Recall:and Now we have so Units??

Examples: 1.What is the energy used by a 10.0 Amp lawn mower that operates for 1 hour using 110 Volts?

2. How long would it take a A) computer monitor operating at 120 V and drawing 0.8 A of current to consume 3.96 MJ of energy? B) heater operating on 240 V drawing 20 A of current?

3. One electron volt (1 eV) is a unit of energy we will used when dealing with elemental particles in Nuclear Physics. 1 eV is the energy given to an electron has its is accelerated through a potential difference of 1 volt. What is the energy equivalent of 1 eV measured in Joules?

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Sources of Electrical Energy: 1. Electrochemical Cells: Chemical potential energy is changed to electrical potential energy in a cell. A chemical reaction that proceeds only one way, where the chemicals gradually become used up is called a primary cell or dry cell. If the chemical reaction is reversible, the cell can be recharged and is called a secondary cell or storage cell. Two or more cells connected together form a battery of cells, or simply a battery.

Examples A)The Voltaic Cell ( named after Alessandro Volta) 1.1 volts not practical because it is easy to spill. a primary cell

B) Dry Cell - an ordinary battery Carbon - ZincZinc- Alkaline

Mercury Cell Watch battery

C) Secondary Cells - rechargeable batteries Examples are: Nickel-Cadmium Silver-Cadmium Nickel-Iron Nickel Metal Hydrate Lithium Ion Lead Acid (car battery)

These batteries (series of cells) can be reused by having another source of electrical energy applied to it. This reverses the chemical reaction.

2.Electromagnetic Generators This is the source of household electricity. If a conductor is moved through a magnetic field the electrons in the conductor experience a force which causes them to move resulting in electric current. The mechanical energy used to move the conductor is converted into electrical energy.

This energy may be from: falling water Example: hydro electricityhydro electricity diesel or gas motors e.g. Campsite Generators Wind e.g. Ramea Wind Diesel ProjectRamea Wind Diesel Project moving steam e.g. nuclear power plantsnuclear power plants the Holyrood electric generating plant

3.Piezoelectricity: Certain crystals such as quartz and Rochelle salt produce electric current if a mechanical force is exerted on it. Examples are : phonograph cartridges, certain radiation detectors some BBQ lighters Also these crystals produce mechanical motion if a electric current is applied to it. An example is a quartz watch.

4.Thermoelectricity: Bi-metal strips of dissimilar metals produce an electric current when the two ends are exposed to different temperatures. They are used in thermometers: –iron-copper can measure between 0o C to 275 o C –platinum-rubidium has a range of 0 o C to 1700 o C (can be used for measuring temperature of molten metal.)

5.Photoelectricity: Converts solar energy into electrical energy. It works because electrons of certain materials ( semiconductors ) absorb light energy so that they are able to move away from their atoms, thus producing electric current. Uses: –satellites – watches – calculators – space probes –space station

What is the most likely source of electrical energy for each of the following: A)a cellular telephone - own battery (dry cell or NiCd) - car's alternator (generator) - lead-acid storage battery B)a digital watch - dry cell C)a car stereo - alternator and lead-acid storage battery

D)a home DVD player - AC generator E)a ship to shore radio - diesel driven generator - wind generator - battery (dry cell or NiCd) F)a communications satellite - solar cells and storage battery G)a phonograph -piezoelectric crystal H)a thermometer used to measure the temperature of hot flue gases - thermocouple

Schematics

No 16 - Churchill Falls 5,429 MW Canada

No 1 - Itaipu 14,750 MW Brazil/Paraguay

Ramea Wind Diesel Project

CANDU 6: Point Lepreau