note (3) Electricity – A form of energy that results from the interaction of charged particles, such as electrons or protons Current Electricity – The flow of electrical charges Static Charge (static electricity) – An electric charge that tends to stay on the surface of an object, rather than flowing away quickly Charging by Friction – A process in which objects made from different materials rub against each other, producing a net static charge on each (net charge = overall charge). The material with a stronger attraction to electrons pulls electrons from the other and becomes negatively charged. The material with a weaker attraction to electrons loses electrons from the other and becomes positively charged. Charging by Contact – Generating a charge on a neutral object by touching it with a charged object Electric Discharge – The rapid transfer of electric charge from 1 object to another. It occurs when 2 objects that have a charge imbalance are brought close together or come into contact. Electrons always move from the object with the more negative charge towards the object with the less negative charge. It could sometimes be seen as sparks Electric Field – A property of the space around a charged object, where the effect of its charge can be felt by other objects Induced Charge Separation – The movement of electrons in a substance caused by the electric field of a nearby charged object, without direct contact between the substance and the object Electroscope – A device for detecting the presence of an electric charge Electrical Energy – Energy provided by the flow of electrons in an electric circuit, which is measured in joules (J) Law of Electric Charges: – Laws that describe how two objects interact electrically when one or both are charged 1. Like charges repel 2. Opposite charges attract 3. Charged and neutral objects attract each other General Other Rules: 1. Protons and neutrons never move or leave the atom. They remain part of the nucleus always. 2. Electrons move and can be transferred from atom to atom. Insulator – A material in which electrons cannot move easily from one atom to another (e.g. rubber) Conductor – A material in which electrons can move easily between atoms (e.g. copper wire) Semiconductor – A material in which electrons can move fairly well between atoms (e.g. humans) Ground – An object that can supply, take, or store a very large number of electrons Electrostatic Series – A list of materials that have been arranged according to their ability to hold on to electrons. When one is rubbed with another, the weaker substance will lose its electrons and become positive. The stronger substance would then gain electrons and become negative. Tends to lose electrons ⇓ ● Acetate ● Glass ● Wool ● Cat’s fur/human hair ● Calcium, magnesium, lead ● Silk ● Aluminum, zinc ● Cotton ● Paraffin wax ● Ebonite ● Polyethylene (Plastic) ● Carbon, copper, nickel ● Rubber ● Sulphur ● Platinum, gold Tends to gain electrons ⇑ General Things to Note: 1. Neutral: # of protons = # of electrons 2. Positive: lose electrons (more protons than electrons) 3. Negative: gain electrons (more electrons than protons) 4. Ebonite rubbed with fur = Ebonite is negative, fur is positive 5. Glass rod rubbed with silk = Glass is positive, silk is negative Electric Circuit: – Closed path along which electrons can flow – has an energy source – electrons flow from one terminal (-ve) of energy source to another terminal (+ve) Switch – A control device that allows the path to be broken, disrupting the flow of electrons (e.g. light switch) – allows the circuit to be closed Open Electric Circuit – A circuit with a break in the flow of electrons How Electrons Move: – When a conductor disconnects from an energy source, its electrons move randomly – the energy source, its electrons move randomly – the energy source produces an excess of electrons at the negative terminal, producing an electric field in the conductor -electric field causes the electrons to move in one direction through the wire – electrons flow through the path of least resistance Electric Current: – Rate of movement of electric charge (flow of electrons) Battery – A connection of 2+ cells Electrochemical Cells – A device capable of generating electrical energy from a chemical reaction Primary Cell – Cell that can only be used once. The chemical reactions use up some of the materials from the cell as electrons flow through it. ● Wet Cell – A cell that contains a liquid electrolyte ○ Electrode – Metal terminal in a cell or battery, usually zinc and copper ○ Electrolyte – A solution or a paste that conducts charge ○ Negative Terminal – The plate in a voltaic cell where electrons collect ○ Positive Terminal – The plate in a voltaic cell where positive charges collect ● Voltaic Cell – A source of electric current energy generated by chemical reactions between two different metals, separated by a conducting solution ● Dry Cell – A cell that functions the same way as a wet cell, but the electrolyte s a moist paste rather than a liquid. Secondary Cell – Cell that can be discharged and recharged many hundreds of times (Rechargeable). 2 chemical processes are involved: 1) One to discharge the cell, and 2) one to recharge it to its original state Fuel Cell – A cell that generates electricity through the chemical reactions of fuel that is stored outside the cell Solar Cell – A cell that converts sunlight into electrical energy Load – A device that transforms electrical energy into heat, motion, sound or light (e.g. toaster, radio, etc.) Series: 1 path for electrons – When there is a break in the series, all loads don’t receive the charge – in series, identical bulbs may not have the same intensity – is used up quickly – ”AND” -stronger intensities of energy, but rate changes per load Parallel: 2+ paths of electrons – when 1 path is off, other parts of the circuit may still be on – if light bulbs are identical in different branches, they have the same intensities – ”OR” -lasts longer – Has consistent power ● Wall outlets & lights are connected in parallel Electron Flow in Conductors: 1. In a conductor not connected to an energy source, electrons move randomly 2. In a conductor connected to a source of electrical energy, the electrons move in one direction through it Electrical Resistance (R) – A conductor’s ability to resist the flow of electrons to some extent (resistance would generally refer to impede the flow of particles in a material) – causes a loss of electric potential Potential Difference (V drop/electric potential) – Difference in the amount of electrical potential after electrons have flowed through the conductor – measured in Voltage (V) Electric Current (I) – Flow of electrical charges – measured in Amperes (A) Resistor – 1. Decreases electrical current through a component by a set amount 2. Used to safely supply a load with needed Volts 3. Reduces current 4. Made of alloys Ohm’s Law – The potential difference between two points on a conductor is proportional to the current flowing V=IR I=V/R R=V/I ● Current (I) – How many e- 's are in a circuit, measured in Amperes (A) ● Voltage/”Electrical Energy” – The amount of energy the e- 's have in a circuit, measured in Volts (V) ● Resistance (R) – The resistance to flow of e- 's through a load, measured in Ohms (Ω) ● I increases as V increases ● I decreases as R increases ● More current = More electrons ● Resistance ⇒ Electrical friction ● Series Circuit: ○ ILoad = ISource (1 current through all loads) ○ VLoad = VSource/#Loads (Energy is dropped at each load) ○ Calculate resistance: Add all the resistances up ● Parallel Circuit: ○ ILoad = ISource/#Loads (Current is shared across all loads) ○ VLoad = VSource (All loads get full energy drop) Short Circuit – +ve & -ve terminals of cell may touch a metal key and complete the circuit with no electrical load to use up battery energy. Key and cell may heat up enough to combust Direct Current (D/C): – The current in which charged particles travel through a circuit in only one direction. Electrons move from the negative terminal to the positive terminal only. Alternating Current (A/C): – The current in which electrons move back and forth in the circuit. It’s caused by moving a magnet into and out of a coil of wire that generates a current. The current moves in one direction when a pole of the magnet is inserted into the coil. The current moves in the opposite direction when the magnet is removed from the coil. Circuit Breaker: – Limits the amount of current to a set value – prevents overheating in wires which leads to electrical fires – placed in series with electrical meter and other breakers – when current exceeds limit, breaker changes shape and opens the circuit, stopping the current flow Fuse: – Function same as circuit breaker – metal conductor melts at a certain current amount, which opens the circuit, stopping the current flow Wall Outlet & Plugs: – Prevent shock from faulty appliances – round plug connects to metal frame of appliance Surge Protector: – Prevents circuit damage during power surges (that can be caused by lightning) – resistance builds in the surge protector when the current exceeds the set limit Power Bar & Switch: – All connected appliances can be turned off with a single switch – parallel outlets – switch is in series with wall outlet Energuide & Energy Star Labels ● In Canada, household appliances must be sold with Energuide label ● Label announces amount of energy used per year, and shows how the appliance model compares to others in its class ● Energy Star helps us save money and protect the environment w/ efficient products and practices ● Proves that the appliance meets the minimum level of efficiency ● 20-30% less energy used than federally required