Devices and systems convert energy with varying efficiencies Chapter 3 Devices and systems convert energy with varying efficiencies

Energy forms and transformations Section 3.1

Energy What is energy? Where do we use energy? How do we convert one type of energy into another?

Energy Energy is defined as the ability to do work It can cause changes to the temperature, shape, speed, or direction of an object http://www.youtube.com/watch?v=pDK2p1QbPKQ

Energy There are four common types of energy: Chemical Electrical Mechanical Thermal

Chemical Energy The energy stored in chemicals This is a form of potential or stored energy It is released when chemicals react

Chemical Energy A common molecule used for the production of energy in humans is glucose, a type of sugar Your cells use glucose molecules and a series of chemical reactions to convert the chemical energy stored in glucose into thermal and mechanical energy Chemical energy from batteries can be converted to electricity and then sound

Chemical Energy Part of the mechanical energy used to demolish this building came from the chemical energy stored in explosives The rest comes from gravitational potential energy

Electrical Energy The energy of charged particles Electrical energy is transferred when electrons travel from one place to another

Mechanical Energy The 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

Mechanical Energy Potential Energy Kinetic Energy Stored energy that can be converted to other, useful forms Kinetic Energy Energy due to motion http://www.youtube.com/watch?v=7K4V0NvUxRg

Thermal Energy The total kinetic energy of all the particles in a substance The faster a particle moves, the more kinetic energy it has; this also means it has more thermal energy (heat) If you were to compare two cups of coffee holding equal amounts of liquid, the one feeling warmer is the one that has the faster moving particles

Transformations Involving Chemical and Electrical Energy You can use various devices to transform electricity into other forms of energy Electricity can be transformed into any other type of energy, such as heat, light, sound, or movement (mechanical energy)

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 joined together that conduct heat a slightly different rates When the metals are heated, this different results in electricity flowing from one metal to the other http://www.youtube.com/watch?v=gtO0kQ-PT_0 (1 min)

Transformations between Thermal and Electrical Energy Devices such as heaters and ovens do the opposite of a thermocouple; they convert electrical energy into thermal energy The electrons flow through a metal and heat up the metal, releasing heat

Examples : Device Stove Burner Hair Dryer Light Bulb Loud Speaker Electric Car Solar Cell Generator Battery Thermocouple Energy Conversion Starting form Final Form Electricity Thermal Thermal/Mech/Sound Light/Thermal Sound Mechanical Light Chemical

Assignment C+R Pg. 323 #1-9

Energy Transformations Involving Electrical and Mechanical Energy Section 3.2

Motors Many of the electrical devices we use everyday contain a motor This important energy converter can be traced back to the early 1800s In 1820 Hans Christian Oersted discovers that current flowing through a wire creates a magnetic field around the wire

Motors Later on, Michael Faraday constructs a device which uses electromagnetic forces to move an object This was effectively the first motor It didn’t work very well, nor did it produce a lot of power, but it showed that electricity could produce continuous motion http://www.youtube.com/watch?v=zOdboRYf1hM

Electric Motors Running electric current through a wire creates a magnetic field. Using this simple principle, many useful devices, such as motor and stereo speakers have been developed. The magnetic field around a wire is circular and continuous

Electric Motors In a piece of wire, the magnetic field generated does not become particularly strong If the wire is coiled around an object (such as a nail), the lines of the magnetic field overlap and the overall field becomes much stronger

Electric Motors The more wraps, the more overlapping, and the stronger the magnetic field The nail becomes an electromagnet when current runs through the wire The stronger the magnetic field, the stronger the magnet However, when the electric current is stopped, the magnetic field collapses, and all magnetic attraction is lost

Electric Motors An electric motor uses electric energy to make a coil of wire spin between the poles of a magnet (the “field magnet”). This occurs because the coil (armature), is connected to a source of electric energy. Current flowing through the coil turns into an electromagnet, which is rotated by magnetic forces from the field magnet. https://www.youtube.com/watch?v=LAtPHANEfQo

Electric Motors The fundamental law of all magnets- opposite poles attract and like poles repel- is the basis upon which electric motors function.

Direct and Alternating Current In one common design for direct current (DC), a rotating wire coil (armature) becomes an electromagnet as current flows into it through a split ring commutator

Direct and Alternating Current The armature is attracted and repelled by stationary field magnets near it, so it begins to rotate. The commutator acts as a switch, cutting off then reversing the direction of current flow to keep the armature turning. Direct Current (DC) - electricity flows in only one direction.

Direct and Alternating Current Alternating Current (AC) - electricity flows back and forth 60 times per second. Large electric generators in power stations produce alternating current for us in homes and industry. Transformers are used to “step up” the voltage for efficient transmission over long distances. https://www.youtube.com/watch?v=BcIDRet787k

At the destination, other transformers “step down” the voltage to the 240/120 V used in homes and factories.

Generators Electric currents can produce magnetic effects. The opposite process is also possible. Electric effects can be produced using a magnet. Michael Faraday and an American scientist named Joseph Henry made this discovery in 1831.

Generators Working independently, they found that a voltage developed in wires that were moved at an angle to a nearby magnet. The same thing happened when the magnet is moved at an angle to a stationary wire. This process is know as electromagnetic induction.

Joseph Henry 1797 - 1878

Generators Electric generators use the relationship between magnetic fields and electric charges to cause charges to move. Any moving electric charge generates a magnetic field, and any moving magnetic field also causes the movement of an electric charge.

Generators Within a generator, a series of magnets is connected to a turbine driven by some other energy source (wind, flowing water, steam, etc.) The magnets in the generator spin relative to a coil of conducting wires. The current then leaves the generator to be used by devices connected to it or it enters the power grid for distribution to a wider area.

Assignment C+R Pg. 331 #2-7, 9-10

Measuring Energy Input and Output Section 3.3

Measuring Energy Input and Output We use energy in every aspect of our lives At home, in our vehicle, at school, etc. How do we know which type of energy is best? How do we know what machines convert energy the best?

Power Power is the rate at which energy is transferred or transformed Power tells you how fast the energy is being used or produced If a machine uses 1 Watt of power, it uses one joule of energy in one second

Power For example, an electric hair dryer that uses 1500 joules of energy every second would be rated at 1500 watts. A light bulb that uses 60 joules of energy every second would be rated at 60 watts.

Math Connect A generator produces 60 J of electric energy in thirty seconds. How many watts of power does it produce? Skills Practice

“Power” Companies What do you buy from power companies? Electric energy The consumption of electric energy is measured in watts. Usually, when you use power you are using it over an extended period of time Energy = power x time (W•h)

Math Connect Watt Hours Skills Practice How much electric energy does a 40 W light bulb use if it is left on for two hours? Skills Practice

Kilowatt Hours The watt hour is a small unit of energy Electric utility companies use a unit of energy 1000x larger, the kW•h 1 kW•h = 1000 W•h (Epcor Bill!)

Math Connect A small kettle is rated at 1000 watts. This means that it uses 1000 watts for each hour it is used. During one week, it is used for two hours. How much energy does it use in kilowatt hours? Skills Practice

Power in circuits How do we calculate the power across the resistor? Step 1. Ohms law to find the Current. Step 2. P = V x I

Law of Conservation of Energy What do you already know about energy?

Conservation of Energy What types of energy are produced by a blow dryer? Thermal energy Mechanical energy Sound energy Light energy Friction produces thermal energy that is wasted If you measured the electric energy that goes into the dryer, and compare it to ALL the forms of output energy, you would find that they are equal

Law of Conservation of Energy Energy cannot be created or destroyed; it can only be transformed from one type to another Energy does not just disappear, if some energy seems to be missing it is because some of it was dissipated to the surroundings Input Energy Output Energy What goes in Must come out

Energy Dissipation Most often the missing energy is lost or dissipated as heat Mechanical systems dissipate energy to their surroundings, and all the “missing” energy is transformed into energy you cannot use

Efficiency and Saving Energy Incandescent light bulbs are designed to convert electric energy into light Incandescent means “glowing with heat” These bulbs produce light when electricity flowing through a wire makes the wire hot Some electricity is converted to light, most of it is converted to other types of energy, such as heat http://www.youtube.com/watch?v=ByCOTG2-mhg

Efficiency Efficiency is a measure of how completely input energy is converted to output energy Incandescent bulbs and fluorescent bulbs produce about the same amount of light; however, incandescent bulbs produce much more heat, which is wasted Therefore, incandescent light bulbs are much less efficient than fluorescent bulbs

Efficiency

Math Connect An electric kettle uses input energy of 240 000 joules to heat water. 196 000 J is actually used to heat the water. Calculate the efficiency of the kettle. Skills Practice

Assignment C+R Pg. 338 #1-10

Reducing the Energy Wasted by Devices Section 3.4

Reducing Waste Energy 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.

Limits to Efficiency Electric heaters come very close to being 100% efficient, but devices that 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.

Increasing Efficiency Increasing the efficiency of a device depends on its purpose Most devices convert electric energy to mechanical energy, where the worst “offender” of waste energy is friction The easiest way to increase the efficiency is to decrease the friction in these devices For devices that produce heat energy, insulation is the way to go Think about your oven Even the fridge – to prevent heat from getting in, you would insulate the fridge better

Assignment C+R Pg. 342 #1-8