electricity
- a form of energy that involves the movement of electrons
| Static Electricity | Current Electricity |
| - the build up of electric charge on an object - some materials gain electrons, some materials lose electrons - maybe natural (i.e. lightning) or man-made |
- the continuous movement of electrons along a pathway or circuit |
Static Electricity
How does it work???
1. Static electricity builds up when 2 different materials are rubbed together.
2. Friction causes electrons to move from one material to the other.
3. The object that gains electrons becomes negatively charged. The object that loses electrons becomes positively charged.
Example
- The balloon and wool are attracted to each other and will cling together
| Gain Electrons | Lose Electrons |
| - rubber - silk - sealing - amber - cotton - plastic (vinyl) |
- wool - glass - fur - acetate |
3 Laws Electricity Charge
1. Opposite charges attract each other.
2. Like charges repel each other.
3. Charged objects attract neutral objects.
Current Electricity
- Current electricity is the continuous movement of electrons along a pathway called a circuit
complete circuit
- electrons are flowing
incomplete circuit
- electrons have stopped moving
- The energy used to make electricity can come from:
Current
current
- the rate at which the electrons flow
ampere
- units used to measure current
galvonmeter
- device that measures weak current
ammeter
- device that measures strong current
Voltage
voltage
- the amount of energy each of the electrons receives
volts
- units used to measure voltage
voltmeter
- device that measures voltage
cell
- device that changes chemical energy into electrical energy (i.e. 1.5V cell)
battery
- 2 or more cells connected together (i.e. 9V battery conatins 6 1.5V cells)
- all cells have 2 things in common:
electrode
- a metal or carbon that allows electrons to enter or leave (conductors)
electrolyte
- a solution that causes a chemical reaction and lets the electrons move from one electrode to the other
Types of Cells
dry cells
- less electrolyte
wet cells
- more electrolyte
Cells / Batteries
Zinc-Carbon Cell
- This is made up of a carbon rod and a zinc casing (2 electrodes) and an electrolyte called ammonium chloride
- Electrons move from (-ve electrode) to the carbon (+ve electrode)
: When the zinc is used, the cell no longer provides energy
- The wet cell works in much the same way. The amount of energy produced depends on the type of electrodes/electrolyte.
| Cell | +ve Electrode | -ve Electrode | Electrolyte | Used |
| Zinc-Carbon | carbon | zinc | ammonium chloride | short-life |
| Alkaline | manganese dioxide | zinc | potassium hydroxide | toys |
| Mercury | mercury | zinc | potassium hydroxide | cameras, watches |
| Lithium | lithium | iodine | P2VP (poly-2-vinyl pyridine) | pace-makers, hearing-aids |
| Nickel-Cadmium | nickel hydroxide | cadmium | potassium hydroxide | rechargeable cells |
| Car Battery | lead | lead | sulfuric acid | rechargeable cars, trucks, tractors |
Resistance
resistance
- a measure of how much a material slows the passage of electrons
resistor
- a device made of a material that slows the flow of electrons
- used in electronics and appliances (toasters, oven, stereos)
: The greater the resistance of a material, the greater the amount of energy give up as they pass through it
light bulb
- is made of thick wires that have low resistance and a thin tungsten wire that has a very high resistance. The thick wire gains little energy from the electrons, heats up and gives off light
Factors that affect Resistance
1. Type of Wire
- Copper offers less resistance than nichrome
2. Thickness of the Wire
- The thinner the wire, the greater the resistance
3. Length of the Wire
- The longer the wire, the greater the resistance (coiled tungsten wire)
4. Temperature
- The greater the temperature, the greater the resistance
generator
- a device that produces electricity from mechanical energy
Two Important Scientists to Remember
1. Hans Christian Oersted
2. Michael Faraday (1831)
Two Types of Generators
simple generators
- devices that produce electricity from the movement of a magnet in and out of a coil of wire (i.e. bicycle dynamo)
commercial generators
- devices that produce electricity from mechanical energy, usually from kinetic energy of steam or running water (i.e. hydroeletric, thermal, nuclear)
| Types of Energy Involved | Forms Change |
| Potential Energy | the type of energy that has the ability to do work |
| Kinetic Energy | the energy of movement |
| Mechanical Energy | the energy of machines as the parts move |
| Electrical Energy | energy produced as the magnet spins around a coil of wire |
Factors that Affect the Amount of Electricity Produced by a Generator
1. The strength of the magnet (the stronger the magnet, the more electricity is produced)
2. The number of coils of wire (the greater the number, the more electricity is produced)
3. The speed of the magnet (the faster the speed [it moves], the more electricity is produced)
alternating current
- a current that flows in one direction and then in the opposite (i.e. magnet moving in and out of a coil of wire)
How do they Produce Electricity (Not in the text!)
Potential to Kinetic to Mechanical to Electrical
Way to remember: Please Kick ME
1. Water is held in a reservoir
(potential energy - has the ability to work)
2. The water is released down a sluiceway / dam
(potential energy to kinetic energy [energy of movement])
3. The water turns the turbines
(kinetic energy to mechanical energy [energy of machines])
4. The turbine shaft turns the electromagnets inside a stationary coil of wire
(mechanical energy to electrical energy)
- Electrical energy moves through external circuits to be stored in the power plant and distributed
Potential (person's leg) to Kinetic (leg peddling) to Mechanical (wheel moving) to Electrical (magnet in coil of wire)
Way to remember: Please Kick ME
1. The magnet is licated in the central drum that rotates
2. The grooved wheel is turned by the wheel of the bicycle, which cause the magnet to turn. (mechanical energy)
3. The coil of wire remains stationary (it does not move)
4. As the magnet turns near the coil of wire, electricty is produced
* If the dynamo is attached to a circuit, electricity is generated as teh magnet spins near the coil of wire
| Themocouple | Solar Cell | Sound |
| - device that consists of a junction of 2 different metals | - a device that converts light energy into electrical energy | - piezoelectric effect: an electric current is produced by sound, when pressure on the crystals (quartz) produce sound waves |
| - electricity is made when the junction is heated or cooled | - photoelectric effect | |
| - heat to electricity | - light to electricity | - sound to electricity (pressure) |
| - i.e. industrial ovens, smoke stacks | - i.e. calculator, solar panels | - i.e. microphone, record player |
| Factors that affect the amount of electricity: 1. Type of material |
Factors that affect the amount of electricity: 1. Strength of light |
Factors that affect the amount of electricity: 2. Type of crystal |
| Piezoelectric Effect | Photoelectric Effect |
| - An electric current is produced by sound, due to the changing pressure of sound waves on certain crystals | - An effect in which light, shining on metal, causes electrons to be emitted from the surface of the metal, producing an electric current |
| - Used in: Microphones |
- Used in: Solar cells |
| i.e. quartz crystals, rochelle salt |
| Series | Parallel |
| - unbranched | - branched |
| - if you increase the number of bulbs, you decrease the current. The bulbs will appear duller | - if you increase the number of bulbs, more current flows in the main circuit and the bulbs receive the same amount of current as if it were the only bulb in an unbranched circuit |
| - resistance using 2 bulbs and one cell is greater than in parallel | - resistance using 2 bulbs and one cell is less than 2 bulbs in series |
| - if you increase the number of cells, the current increases and the bulb will appear brighter | - if you increase the number of cells, the bulb will be brighter |
alternating current
- a current which flows on one direction and then in the opposite direction (i.e. the movement of a magnet in and out of a coil of wire)
direct current
- a current that flows in one direction (i.e. cell to wire to bulb to back to cell)
Circuit Symbols
One Cell
Two Cells
Conducting Wire
Switch
Galvonometer
Closed Switch
Coil of Wire
Voltmeter
Ammeter
Resistor
Bulb 1
Bulb 2
Motor 1
Motor 2
Variable Resistor
:
| Series Circuit | Parallel Circuit |
| - an electric circuit with ONE conducting path and NO branches | - an electric circuit that provides more than one conducting path for electric current |
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 |
- Conducting path for an electrical current
open circuit (incomplete)
- an electric circuit in which the conducting path is broken or incomplete (controlled by a switch that is up)
closed circuit (complete)
- a circuit in which there is an uninerrupted conducting path for the electric current (controlled by a switch which is down)
switches
- devices that can open of close an electric circuit (types: rheostat, two-way, magnetic, timer)