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Written Assessment 1 What is Electricity Electrical Charge ★ Electricity is the interaction of Electric Charges - Fundamental property of protons and electrons, which make up every atom - Protons = positive charge - Electrons = negative charge ★ Law of Electric Charges...

Written Assessment 1 What is Electricity Electrical Charge ★ Electricity is the interaction of Electric Charges - Fundamental property of protons and electrons, which make up every atom - Protons = positive charge - Electrons = negative charge ★ Law of Electric Charges - Electric force is the attraction or repulsion between objects Coulomb’s Law - Size of charges and the distance between them determine the strength of the electrical force between charged objects ★ Static Electricity: The build-up of electric charges on an object - Electrons from one object are attracted to the positive charge of an object. Since the electrons go to the other object (hair’s electrons go to the balloon), the main object (hair) is positively charged while the other object is negatively charged. They are attracted because of the opposite charges ★ Electrical Discharge - Charges that build up on one object move off the object - Sudden and brief flow - Hurts when electrons leave you - You charged = you negative 🌩️ - Example: 🌆 💥 Negative: lighting, cloud Positive: Earth = Electrical Current ★ Current Electricity is a continuous flow of electric charge - Current: quantity of charge that flows past a given point per unit of time (ampere/A) Direct Current (DC): - Charges flow in one direction only - Hard to make and expensive 1  - Example: batteries Alternating Current (AC): - Flow in one direction then the reverse direction, repeatedly - Cheaper but dangerous - Example: current supplied by power companies to homes ★ Conductions & Insulators Conductors: allow an electric current to flow through easily - Metals: copper, aluminum, silver, gold - Water (when it contains dissolved salts or other charged particles) - Graphite (in pencil) - Human body (can conduct small amounts of electric current) Insulators: resist the flow of electric current - Rubber, Glass, Plastic, Air, Wood, Paper 2 Electricity & Magnetism Oersted’s Discovery ★ Hans Christian Oersted (1820): Danish physicist and chemist - First to discover that electric current produces a magnetic field around a wire Electromagnets A coil of wire around an iron rod Current passing through the coils of wire magnetizes the rod, producing an electromagnet (powerful magnet) More loops in the coil = stronger magnetic field Examples: electric motors, loudspeakers, television sets, doorbells, trains, etc. Faraday’s Discovery ★ Michael Faraday’s Electromagnetic Induction Process of creating an electric current by moving a conductor through a magnetic field or by varying the magnetic field around it. Change in the strength of a magnetic field “magnetic flux” induces a current, which induces EMF (Electromotive Force) - Emf is proportional to the rate of change of the magnetic flux Example: the majority of the electricity supplied to homes ★ Magnetic FLux 2 1 Wb (Weber) = 1𝑇 · 𝑚 - Magnetic Field Intensity: Flux per unit area of a loop wire perpendicular to the field - T = Tesla = magnetic field intensity’s SI unit Named after Serbian-American engineer Nikola Tesla Equivalent to 𝑁/𝐴 · 𝑚 = newton per ampere-meter Magnetic Flux can be obtained using: Φ = 𝐵𝐴𝑐𝑜𝑠θ - B = magnetic field intensity Unit: T - Φ = magnetic flux - A = area - θ = angle between the magnetic field and a line perpendicular to the area 3 Lenz’s Law ★ Heinrich Hertz’s Law - The direction of the electric current induced in a conductor by a changing magnetic field - The magnetic field created by the induced current opposes changes in the initial magnetic field Faraday + Lenz’s Law Equation △Φ ★ 𝐸 =− 𝑁 △𝑡 ∆Φ𝑓𝑖𝑛𝑎𝑙−Φ𝑖𝑛𝑖𝑡𝑖𝑎𝑙 - Whole equation for easier memory: 𝐸 =− 𝑁 ∆𝑡 - E = induced Electromotive Force (EMF) - △Φ = change in magnetic flux = Φ𝑓𝑖𝑛𝑎𝑙 − Φ𝑖𝑛𝑖𝑡𝑖𝑎𝑙 - ∆𝑡 = time elapsed - Negative sign: induced EMF sends current in a direction that opposes the change the magnetic flux is causing 4 Electric Generator Basic Parts of an AC and DC Generator ★ Alternating Current “AC” Generator Magnets - A magnetic field is needed to produce electricity - Its relationship with the coils produces the electrical field - Either actual permanent magnets or a second set of coils Armature Coil - Voltage is produced - Consists of wires (the coils) that carry the full load current of the generator - Built in stator (normally) 2 Slip Rings - Used to transfer electrical power from stator to circuit - Usually made of conductive stuff (copper, brass, etc.) - Also called rotary electrical interface - Connected to windings 2 Carbon Brushes - Makes contact with slip rings - Conducts an electric current Load - the thing being powered by the generator - the ‘demand’ for the electrical power of the generator - devices ★ Direct Current “DC” Generator Magnets - The stator - Faces opposite each other Armature Coil - Also called armature windings (windings is multiple coils) - In a closed-circuit form - Connected in series to enhance the sum of the current - Built in rotor 5  Slip Rings (Commutator) - Changes the AC voltage to DC within the armature coils - Designed with copper segments/parts (mica sheets ‘protect’ each segment) - Located on the shaft of the machine Carbon Brushes - Collects current from slip rings - made up of carbon and graphite to reduce the wear and tear of the slip rings - When on a segment, the brush shorts out that segment/coil and gets current from the other coils Load - Stuff that is powered by DC power - Includes batteries, gadgets, some LED lights, etc. How do generators work? ★ Mechanical Energy is transformed into electrical energy ★ Principles of all generators are the same except for some differences in the construction ★ 2 Main Parts: Coil & Magnet - The generator works on Faraday’s Law of Electromagnetic Induction. When the coil is rotated in a magnetic field by some mechanical means, magnetic flux is changed through the coil and consequently, Electromotive Force (EMF) is induced in the coil. 6 Electric Power Production and Distribution How do power plants produce large amounts of electricity? ★ The generation, transmission, and distribution of electric power are called power system - Stages: 1. Generation 2. Transmission 3. Distribution ★ Most transmission lines are high-voltage three-phase alternating current (AC) ★ High-voltage direct-current (HVDC) technology is used for greater efficiency over every long distance (typically hundreds of miles) ★ Electricity is transmitted at high voltages (115kV or above) to reduce the energy loss that occurs in long-distance transmission Stages and layout of power systems 1. Power Station - Bulk power is generated by 3-phase, 3-wire system employing several alternators in parallel - Voltage: 11kV - Due to economic considerations, the generator voltage (11kV) is stepped up to 220kV or 132kV at the power station with the help of step-up transformers. 2. Primary Transmission - High voltages of the order: 66kV, 132kV, 220kV, and 400kV - Used for transmitting power by 3 phase 3 wire overhead system - Supplied to substations on the outskirts of major distribution centre or city 3. Secondary Transmission - Outskirt of the city - Sub-station steps down the primary transmission voltage to 66kV or 33kV - Power is transmitted at this voltage - 3 phase wire system used 4. Primary Distribution - Transmission lines or inner connectors terminate at large main substations - Power is distributed to small secondary substations scattered throughout the load area - Voltage range: 11kV to 132kV 7  5. Secondary Distribution - Low-voltage networks laid along the streets; localities and over the rural areas - Connection to individual customers - The circuit used for this purpose is 3 phase 4 wire, 440V/220V from which either 3-phase 400V or single-phase 220V supply to the consumers may be provided. Transformers Types of Transformers - Process always starts from left to right so we know when the transformer is step-up or step-down on the number of coils on the left side (Primary Coil) of the transformer - 1:3 ratio Step-down transformers - Primary coil is more than secondary coil - Primary coil/Primary Winding: electrical wire wrapped around the input side Step-up Transformer - Primary coil is less than the secondary coil 1:3 ratio Primary coil: 40 Secondary coil: 120 - Secondary Coil/Secondary Winding: electrical wire wrapped around the output side How do transformers work? ★ Transformer Operation - Electrical transformer consists of a ferromagnetic core and two coils called “windings” 8  - Uses the principle of mutual inductance to create an AC voltage in the secondary coil from the alternating electric current flowing through the primary coil. - Voltage induced in the secondary coil can be used to drive a load ★ What is Mutual Inductance - Two electrical coils are placed near each other - AC electrical current flowing in one coil induces an AC voltage in the other coil Current in the first coil creates a magnetic field around the first coil which induces a voltage in the second coil The transformer improves the efficiency of the transfer of energy from one coil to another by using a core to concentrate the magnetic field The primary coil creates a magnetic field that is concentrated by the core and induces a voltage in the secondary coil ★ Turns Ratio (TR) - Voltage at the secondary coil can be different from the voltage at the primary coil Number of turns of the coil in primary and secondary are not the same - Ratio of the number of turns in the primary coil to the number of turns in the secondary coil Turns Ratio Formula 𝑁𝑃 𝑛𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑡𝑢𝑟𝑛𝑠 𝑖𝑛 𝑡ℎ𝑒 𝑝𝑟𝑖𝑚𝑎𝑟𝑦 - 𝑇𝑅 = 𝑁𝑆 = 𝑛𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑡𝑢𝑟𝑛𝑠 𝑖𝑛 𝑡ℎ𝑒 𝑠𝑒𝑐𝑜𝑛𝑑𝑎𝑟𝑦 Transformer Output Voltage Formula 𝑉𝑃 𝑃𝑟𝑖𝑚𝑎𝑟𝑦 𝑉𝑜𝑙𝑡𝑎𝑔𝑒 (𝑉𝑜𝑙𝑡𝑠) - 𝑉𝑆 = 𝑇𝑅 = 𝑇𝑢𝑟𝑛𝑠 𝑅𝑎𝑡𝑖𝑜 𝑉𝑆 = secondary voltage (Volts) ★ Transformer Voltages & Currents 9  𝑉𝑃 𝐼𝑆 𝑁𝑃 - 𝑉𝑆 = 𝐼𝑃 = 𝑁𝑆 𝐼𝑆 = Induced Secondary 𝐼𝑃 = Induced Primary 10 Electric Motor Basic Parts of an AC and DC Motor + How do Electric Motors Work? - A generator operating in reverse: changes electrical energy to mechanical energy ★ DC Motor - DC Generators can be used as DC motors, so DC motors have the same parts as a simple DC generator Simple DC Motor - Brushes are connected to a battery to send current to the armature - Magnetic field produced by this current interacts with the field of the magnet and exert a force that rotates the armature. Rotation = electric current creates 1 magnetic field to interact with the magnetic field of the magnets - A shaft attached to the armature makes the rotational motion available for doing work - Rotor coils - Commutator: changes current - Shaft - Brush - Stator magnet Brushed DC Motor - Armature “rotor”: connected with the electromagnet rotates - Permanent magnets are stationary “stators” Brushless/Emerging DC Motor - No brushes or commutator - Electronically commutated - Permanent magnets are glued to the rotor - Electromagnets are part of the stator - Used in computer cooling fans ★ AC Motor - No brushes or commutator - Two coils similar to a transformer Electromagnetic induction transfers energy between the two coils causing the second coil to spin 11