Science 9 Unit D Electrical Principles Topic 3.0

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1 Science 9 Unit D Electrical Principles Topic 3.0 Energy is all around us in many different forms light from lamps, sound from stereos, heat from furnaces and stoves. Yet we rarely think about how much energy we use in a day. It has been estimated that it would take 2800 hours of strenuous manual labour to produce as much energy as a typical Canadian uses daily. You would need a team of 350 people working for eight hours straight to supply the energy for just one person. Kinetic Energy: is the energy which it possesses due to its motion Potential Energy: is the energy stored in a body or in a system due to its position in a force field such as gravity. A spring has more potential energy when it is compressed or stretched. A steel ball has more potential energy raised above the ground than it has after falling to the Earth. In the raised position it is capable of doing more work. The newton is the SI unit for force named after Isaac Newton It is equal to the amount of force required to accelerate a mass of one kilogram at a rate of one meter per second squared 1 N is the force of Earth's gravity on a mass of about 102 g - such as a small apple. The scientific definition of a force is a push or pull upon an object F (Force) = m (mass) X a (acceleration) Force is measured in Newtons 1 Newton = 1 kg-m or 1 kilogram-meter per second squared s 2 An object has a mass of kg and an acceleration of m/s 2. What is the force on the object? The Joule Englishman James Joule ( ) contributed greatly to our understanding of energy by proving that both mechanical work and electricity can produce heat and vice versa. In recognition of the importance of his research, scientists named the unit of energy the joule (J). It is equal to the work done in applying a force of one newton through a distance of one metre In electrical terms it is the work required to produce 1 watt of power for one second 1 J = 1 W per 1 s or J = W x s Work - when a force causes an object to move in the same direction of the force being exerted on it. W (Work) = F (force) X D (distance)

2 How much work is done by a person who uses a force of 27.5N to move a grocery buggy 12.3m? W (Work) = F (force) X D (distance) 55, 000J of work is done to move a rock 25m. How much force was applied? You and 3 friends apply a combined force of 489.5N to push a piano. The amount of work done is J. What distance did the piano move? Watts - named after the Scottish engineer James Watt Power (W) = J s The unit, defined as one joule per second, measures the rate of energy conversion. The terms power and energy are frequently confused. Energy is defined as the amount of work that can be performed by force measured in Joules or kilowatt hours. Power is the rate at which energy is generated or consumed measured in watts. 1 watt is equal to 1 joule per 1 second. When charging for electricity we use kilowatt/hours A unit of energy is kilowatt hour W per 3600 s When a 100W light bulb is turned on for one hour, how much energy is used? How many kilowatt hours of electricity are used? (first convert watts to kilowatts) Then calculate kilowatt hours In Alberta we pay about 10 cents per kilowatt hour. What would it cost for to use a 100 W bulb for 1 hour? Cost = kwh X rate (d dollar)

3 A microwave oven has a power rating of 800 W. If you cook a roast in this oven for 30 min at high, how many joules of electrical energy are converted into heat by the microwave? A hair dryer has a power rating of 1500 W. If you use it for 10 min, how many joules of electrical energy are converted into heat by the hair dryer? ELECTRICAL POWER Power is the rate at which a device converts energy. The faster a device converts energy, the greater its power rating. For an electrical device, the power is the current multiplied by the voltage. Mathematically, the relationship between power (P), current (I), and voltage (V) is Power (W) = I (A) x V watts = amperes x volts Think of our model using waterfalls. The power of a waterfall is equal to the amount of water flowing times the difference in potential energy between the top of the falls and the bottom. (P) Power in watts (I) current in amperes (V) voltage in volts Power (W)= I x V I = W V V = W I A hair dryer uses 10 A of current plugged into a 120 V outlet. What is the power of the hair dryer? A hair dryer has a power rating of 600 W. It is plugged into a 120-V outlet. What is the current flowing through the hair dryer?

4 A hair dryer has a power rating of 600 W uses 10 A of current. What is the voltage of the hair dryer? Kilowatt Hours It doesn t take common electrical devices long to consume a large number of joules. For this reason, the kilowatt hour is often used as a unit for energy. The energy calculation is the same, except that hours are substituted for seconds, and kilowatts (kw) are substituted for watts. Appliance Watts Appliance Watts Coffee Pot 200 Ceiling Fan 50 Toaster 1000 Blow Dryer 1000 Electric Stove 4000 Computer - laptop 50 Blender 300 Computer - desktop 100 Microwave 1000 Refrigerator 112 Hot Plate 1200 Satellite Dish 30 Sewing Machine 100 Plasma TV Calculate how much it would cost to bake a cake for 2 hours in in an electric stove (4000 W). First calculate the kw then calculate the kwh then calculate the cost

5 Energy has a number of different forms. Thermal, or heat energy: The total energy of a substance particles due to their movement or vibrations also the energy of motion in the molecules of a substance. The faster a particle moves, the more kinetic energy it has. Compare two cups holding equal amounts of water: the one containing more thermal energy will feel warmer. Electrical Energy: Energy made available by the flow of electric charge through a conductor. Mechanical Energy: Energy possessed by an object because of its motion or its potential to move. A thrown baseball has mechanical energy because of its movement and its potential to fall. Electromagnetic Energy (light): Energy packets called photons. It is electromagnetic radiation with a wavelength that is visible to the eye. Sound Energy: Energy produced by vibrating objects than can be detected by the ear.sound energy can travel through substances such as, water, air, wood, or fire. Nuclear Energy: Energy released by a nuclear reaction by fission or fusion Chemical Energy Energy found in chemicals, including food. Glucose molecules are used in your body cells to produce thermal energy and mechanical energy. Cellular Respiration

6 Transformations Involving Chemical and Electrical Energy Examples of Devices That Convert Energy from One Form to Another Input Energy Device Output Energy electrical toaster chemical flashlight electrical blender chemical battery-operated clock Electric Motors Motors have a place in many of the electrical devices that we use every day. The beginnings of this important energy converter the motor can be traced back to the early 1800s. Oersted had discovered that current flowing through a wire creates a magnetic field around the wire. Eleven years later, Michael Faraday constructed a device that used electromagnetic forces to move an object. In Faraday s device, a hanging wire circled around a fixed magnet Faraday also made a device in which a magnet rotated around a fixed wire. Faraday s devices led to the development of the electric motors that we use. Early experimenters found that they could make a strong electromagnet by winding currentcarrying wire into a coil usually around an iron core. They also found that an electromagnet will move to line up with the magnetic field from a nearby permanent magnet. This is the same way that two permanent magnets attract each other.

7 Many electric motors use a commutator and brushes to reverse the flow of electricity through the electromagnetic coil. The commutator is a split ring that breaks the flow of electricity for a moment and then reverses the connection of the coil. When the contact is broken, so is the magnetic force. But the armature continues to spin because of its momentum. The armature is the rotating shaft with the coil wrapped around it. As a result of the spinning, the commutator reconnects with the brushes. The magnetic force on the coil keeps it spinning continuously. The brushes are usually bars of carbon pushed against the metal commutator by springs. They make electrical contact with the moving commutator by brushing against it Vacuum Cleaner Vacuum cleaners work with the help of an electric motor. The motor has a fan attached. When it spins, the blades of the fan force air out, which creates suction inside the vacuum cleaner. Air from the room forces its way into the vacuum, carrying dirt with it. DIRECT AND ALTERNATING CURRENT Some motors run on direct current (DC). It s called direct current because the electricity flows in only one direction. Many devices such as ipods, computers, cell phones, and calculators also use DC. The electricity in your household circuits is alternating current (AC). It s called alternating because it flows back and forth 60 times per second. Plug-in devices that require DC come with their own power supplies. The power supply converts the power company s 120-V AC to DC and supplies the voltage that the device requires. Generating DC and AC A DC generator is much the same as a DC motor. The spinning armature produces the electricity (if electricity is passed through a DC generator, it will spin like a motor). The central axle of an AC generator has a loop of wire attached to two slip rings. The current is switched as the loops move up and down alternatively through the magnetic field.

8 The slip rings conduct the alternating current to the circuit through the brushes (the brush and ring assembly allows the whole loop to spin freely). In large AC generators many loops of wire are wrapped around an iron core. Massive coils of wire rotating in huge generators can produce enough electricity to power an entire city. Electric Lights Incandescent Light What used to be a "normal light bulb" is also known as an incandescent light bulb. These bulbs have a very thin tungsten filament that is housed inside a glass sphere. They typically come in sizes like "60 watt," "75 watt," "100 watt" and so on. Electricity runs through the filament. Because the filament is so thin, it offers a good bit of resistance to the electricity, and this resistance turns electrical energy into heat. The heat is enough to make the filament white hot, and the "white" part is light. The filament glows because of the heat - it incandesces. Fluorescent Light A fluorescent bulb uses a completely different method to produce light. There are electrodes at both ends of a fluorescent tube, and a gas containing argon and mercury vapor is inside the tube. A stream of electrons flows through the gas from one electrode to the other in a manner similar to the stream of electrons in a cathode ray tube. These electrons bump into the mercury atoms and excite them. As the mercury atoms move from the excited state back to the unexcited state, they give off ultraviolet photons. These photons hit the phosphor coating the inside of the fluorescent tube, and this phosphor creates visible light. The phosphor fluoresces to produce light.

9 Compact Fluorescent Light A compact fluorescent lamp (CFL), is a fluorescent lamp designed to replace an incandescent lamp. The lamps use a tube which is curved or folded to fit into the space of an incandescent bulb, and a compact electronic ballast in the base of the lamp. CFLs use one-fifth to one-third the electric power, and last eight to fifteen times longer. A CFL has a higher purchase price than an incandescent lamp, but can save over five times its purchase price in electricity costs over the lamp's lifetime. Like all fluorescent lamps, CFLs contain toxic mercury which complicates their disposal. Light-emitting diode (LED s) An LED lamp is a light-emitting diode (LED) product that is assembled into a lamp (or light bulb) for use in lighting fixtures. LED lamps have a lifespan and electrical efficiency that is several times better than incandescent lamps, and significantly better than most fluorescent lamps, with some chips able to emit more than 100 lumens per watt. The LED lamp market is projected to grow more than 12-fold over the next decade Energy Dissipation Energy is neither created nor destroyed. It doesn't appear and then disappear, but transformed from one form to another. This is known as the Law of Conservation of Energy. No device is able to be 100% efficient in transforming energy. Most often, the energy is lost, or dissipated as heat. Mechanical systems also dissipate energy to their surroundings, but not as obvious as the heat loss. Much of the dissipated energy is sound. Measuring Energy Input and Output We use energy in every aspect of our daily lives driving to work or school, heating our homes, preparing our food, texting, or watching television. Sometimes, we can choose which kind of energy we will use. For example, we could use electricity, gasoline, natural gas, propane, or hydrogen to power a vehicle. But how do we know which is best? To determine that, we need to measure the types and amounts of energy going into and coming out of the devices we use. Understanding Efficiency The efficiency of a device is the ratio of the useful energy that comes out of a device to the total energy that went in. The more input energy converted to output energy, the more efficient the device is. % Efficiency = Joules of useful output x 100% Joules of input energy Most of the energy transformed in a light bulb is wasted as heat. (5% is light energy, while 95% is heat)

10 A 330 W hot plate produces 38 kj of thermal energy while operating for 2 min. What is the efficiency of this device? Calculate the input energy first Input Useful Device Energy Output Gasoline- powered sport utility vehicle 675 kj 81 kj Efficiency Gasoline- electric hybrid vehicle 675 kj 195 kj Mid- efficiency natural- gas furnace 110 MJ 85 MJ Electric baseboard heater 9.5 kj 9.5 kj Alkaline dry cell kj kj Fluorescent light 50 kj 10 kj Incandescent light 800 J 40 J Increasing Efficiency Increasing the efficiency of a device depends on its purpose. The easiest way to increase efficiency in many devices is to reduce friction, as much as possible. Insulating a device from heat loss is also another practical way to increase efficiency. Using capacitors in electrical circuits is also another way to increase efficiency. Capacitors store a charge and then release it smoothing out the supply of electricity Limits to Efficiency Electric heaters come very close to being 100% efficient, but devices which convert electricity to other forms can never be 100% efficient. Some energy is lost, or dissipated in a form that is not useful output. Friction causes thermal energy to be lost, or dissipated in many devices. Power Distribution Grid Electrical power is a little bit like the air you breathe: You don't really think about it until it is missing. Power travels from the power plant to your house through an amazing system called the power distribution grid.

11 The Power Plant Electrical power starts at the power plant. In almost all cases, the power plant consists of a spinning electrical generator. Something has to spin that generator -- it might be a water wheel in a hydroelectric dam, a large diesel engine or a gas turbine. But in most cases, the thing spinning the generator is a steam turbine. The steam might be created by burning coal, oil or natural gas. Or the steam may come from a nuclear reactor. The Power Plant: Alternating Current Single-phase power is what you have in your house. You generally talk about household electrical service as single-phase, 120-volt AC service. The rate of oscillation for the sine wave is 60 cycles per second. AC has at least three advantages over DC in a power distribution grid: 1.Large electrical generators happen to generate AC naturally, so conversion to DC would involve an extra step. 2.Transformers must have alternating current to operate, and we will see that the power distribution grid depends on transformers. 3.It is easy to convert AC to DC but expensive to convert DC to AC, so if you were going to pick one or the other AC would be the better choice. In 3-phase power, at any given moment one of the three phases is nearing a peak. High-power 3-phase motors (used in industrial applications) and things like 3-phase welding equipment therefore have even power output. The three-phase power leaves the generator and enters a transmission substation at the power plant. The substation uses large transformers to convert the generator's voltage (which is at the thousands of volts level) up to extremely high voltages for long-distance transmission on the transmission grid. Typical voltages for long distance transmission are in the range of 155,000 to 765,000 volts in order to reduce line losses. A typical maximum transmission distance is about 300 miles (483 km). All power towers like this have three wires for the three phases. Many towers, like the ones shown above, have extra wires running along the tops of the towers. These are ground wires and are there primarily in an attempt to attract lightning.

12 For power to be useful in a home or business, it comes off the transmission grid and is stepped-down to the distribution grid Transformers are used to change the amount of voltage with hardly any energy loss. Voltage change is necessary because the most efficient way to transmit current over long distances is at high voltage and then reduced when it reaches its destination, where it will be used. A step-up transformer increases voltage, while a step-down transformer reduces voltage. Over drying Millions of dollars of energy are wasted each year running clothes dryers to heat clothes that are already dry. Over drying does nothing for your clothes.over drying creates static cling and contributesto shrinking and fabric damage. The solution? Cut down on drying time. Your clothes and electric bill will look a lot better! Devices, which have an energy-efficient design, are an important consideration for the consumer, because these devices use less electricity. Energy costs money and it also affects the environment, so reducing energy consumption is a good practice. Electrical Safety In many places, power lines and towers were knocked down. Such situations can be extremely dangerous because power lines carry electrons at thousands of volts - enough to seriously injure or kill anyone who comes close to them. You should never approach a downed power line. Any person coming in contact with a power line may create an unintended path for the electricity. Such a path is sometimes called a short circuit because the current bypasses part of the normal circuit. The Dangers of Electrical Shock High voltage power lines can carry 50,000 V of electricity. However, amperage is more important to consider A (1 milliamp) - will likely not be felt at all A to A (15 to 20 milliamps) - will cause a painful shock and loss of muscle control (which means you will not be able to let go of the line) A to A (30 to 50 milliamps) - Increasing pain breathing may become difficult Current as low as 0.1 A (100 milliamps) - can be fatal. Electrical Dangers vary, depending on the situation. When the current can flow easily, it is more dangerous. Insulators (such as wood, rubber and air) hamper the flow of electricity. Moisture is a good conductor of electricity, so avoid water when working with electricity. Protecting Yourself From Electrical Shock The Canadian Standards Council issues labels to identify the amount of voltage required to operate electrical devices and the maximum current they use.

13 Electrical Safety Pointers Never handle electrical devices if you are wet or near water Don't use devices that have a frayed or exposed power cord Always unplug an electrical device before disassembling it Don't put anything into an electrical outlet - except a proper plug for an electrical device Don't overload an electrical circuit, by trying to operate too many devices at once Avoid power lines Don't bypass safety precautions when you are in a hurry Pull on the plug, not the wire Never remove the third prong from a 3 prong plug Fuses and circuit breakers interrupt a circuit when there is too much current flowing through it. Circuit breakers trip a spring mechanism, which shuts off the flow of electricity through the circuit, when there is too much current. It can be reused over and over (provided the cause of the increased flow is corrected). Transformations Between Thermal and Electrical Energy A thermocouple is a device that can convert thermal energy into electrical energy. It consists of two different metals (bimetal) joined together that conduct heat at slightly different rates. When heated, the difference in conduction results in electricity flowing from one metal to the other. Thermocouples are useful for measuring temperatures in areas that are difficult to access or too hot for a regular liquid-filled thermometer. For example, some Alberta farmers hang thermocouple cables in their grain bins. The amount of electricity the cable produces indicates whether the grain is getting too hot. This can happen if the grain is too moist. Ovens and heaters do the opposite. They convert electrical energy into thermal energy.