Section 3 1 Energy Forms and Transformations Nature

Section 3. 1 Energy Forms and Transformations

Nature of Energy is all around you. • You hear energy as sound, you see energy as light, you can feel energy in wind. • Living organisms need energy for growth and movement. • You use energy when you hit a tennis ball, compress a spring, or lift a grocery bag. • Energy is the ability to do work.

Energy The energy released by a supernova is capable of destroying a nearby solar system in just a few hours. A supernova is one of the greatest concentrations of energy in the universe.

• It is estimated that it would take approx. 2800 h of strenuous manual labor to produce as much energy as one average Canadian uses in one day. • In other words: A team of 350 strong people working 8 h straight!

James Joule (1818 -1889) • Studied energy • He proved that mechanical work and electricity can produce heat and viceversa • Unit of measure for energy = the Joule (J)

There are Four Common forms of energy: 1. Chemical Energy • Energy stored in chemicals and released when chemicals react • It is potential or stored energy in foods, fuels, batteries, and explosives • Eg. Digesting food…bonds are broken to release energy for your body to store and use.

2. Electric Energy The energy of charged particles. Electrical energy is transferred when electrons travel from place to place Examples: • Power lines carry electricity • Electric motors • electric appliances

3. Mechanical Energy -Energy of motion. -The energy possessed by an object because of its motion or its potential to move. Examples: Water in a waterfall, Wind, Moving vehicles, Sound, hammer hitting nail

4. Thermal Energy • Total kinetic energy of all the particles in a substance. • The faster a particle moves the more kinetic energy it has. Examples: Friction Changes in state of matter

Thermal Energy • TWO CUP ANALOGY: Compare two cups holding equal amounts of water: the one containing more thermal energy will feel warmer

Energy Conversions • All forms of energy can be converted to other forms. • Law of Conservation of Energy: Energy cannot be created or destroyed.

TRANSFORMATIONS OF ENERGY What energy transformations are taking place? EXAMPLE 1: • place in this picture?

• Chemical energy in the baby’s muscles are being converted into mechanical energy (motion) of the lawn mower • Chemical energy is also being converted into thermal energy as her muscles strain to push the lawnmower.

• Example 2 What energy transformations are taking place with this electric kettle? Electric energy to Thermal energy

Example 3 • What energy transformations occur when listening to music with a discman? Chemical Energy Mechanical Energy Sound Energy

Transformations Involving Chemical and Electrical Energy : Examples of Devices that convert Energy from one form to another include: Input Energy Device Output Energy electrical toaster thermal chemical flashlight electrical, then light and thermal electrical blender mechanical chemical battery-operated clock electrical, mechanical and sound

Thermocouple: A device that converts thermal energy to electricity. – Made of 2 different metals (bimetal) joined together that conduct heat at slightly different rates. – When heated the difference in conductivity results in electricity flowing from one metal to the other. – The higher the temperature difference between the two metals, the greater the amount of electricity produced.

A Thermocouple can be used as a thermometer in extreme high temps. or difficult to access places.

OTEC (Ocean Thermal Energy Conversion) • Scientists are currently researching ways to use the Ocean’s natural thermal energy differences to generate electricity. • Q: what is the temp difference between the surface and the bottom? (p. 323)

OTEC

• Now do Check and Reflect P. 323 #1 -9

Section 3. 2 Energy Transformations Involving Electrical and Mechanical Energy

1820: The Hans Christian Oersted Demonstration • A compass needle is deflected by the magnetic field of a current carrying wire. • He proved that a current flowing through a wire creates a magnetic field around the wire.

1831: Michael Faraday produces first electric motor, proving that electromagnetic forces could produce continuous motion.

Getting Your Motor Runnin’ How a motor works

Types of Magnets 1. Permanent magnet- a hard steel alloy which remains magnetized for a long period of time (like fridge magnets) 2. Electromagnet - a coil of wire (usually with an iron core ) which when attached to a current has magnetic effects. Advantage: you can turn it off and on… like the ones used at car impounds/ wreckers)

Yes, if you wrap a piece of metal in a currentcarrying wire you get…an ELECTROMAGNET!!!! 1. Wrap a piece of metal in wire 2. Hook the wires up to a battery 3. Reversing the wires, reverses the current AND reverses the polarity of the magnet.

A simple Electric Motor requires the interaction of a permanent magnet and an electromagnet. Strong electromagnets are made by winding wire into a coil around an iron core. How do you keep an electromagnet spinning in a magnetic field to make the motor run? Let’s look at the St. Louis Motor…

St. Louis Motor brushes Split-ring commutator Permanent Magnets how a motor works armature

Parts of the motor: • Armature - the rotating shaft with the coil wrapped around it • Commutator - a split ring that breaks the flow of electricity for a moment and then reverses the flow in the coil, when the contact is broken, so is the magnetic field • Brushes - reverse the flow of electricity through the electromagnetic coil – make contact with commutator by “brushing” against it

• The poles of the armature attracted to the opposite poles of the permanent magnet • They spin toward it. • At 180˚, the contact is broken and the poles are reversed. • The split-ring commutator breaks the flow of electricity for a moment and then reverses the current flow in the coil What does changing the polarity do? • This keeps the motor spinning in one direction.

• The armature (the rotating shaft with the coil wrapped around it) continues to spin because of momentum, allowing the brushes to come into contact once again with the commutator. • The poles keep being reversed as the current flow is reversed through the coil thus continuously turning the motor.

Explain the steering wheel analogy to show the split-ring commutator helps the armature spin continuously. (p. 328)

AC or DC Current DC = direct current AC = alternating current Electrons flow one way Electrons move back and forth 60 times/s Most battery operated things use DC Wall outlets AC allows electricity to travel without much loss of energy

Transformers

Transformers No! Not those transformers!

Transformers Power companies generate AC power because with AC, transformers can be used to change the amount of voltage with minimal energy loss.

Some transmission lines carry 500 000 V. This needs to be reduced before it can be used in your home.

Transformers: a current-carrying wire is wrapped around one side of an iron ring called a core. This is the primary coil. - A secondary coil of wire is wrapped around the other side of the core. - Current flowing through the primary coil generates an electromagnetic field which induces a current in the secondary coil.

1. Step-down Transformers - reduce voltage • More windings on the primary coil. • Fewer windings on the secondary coil.

2. Step-up Transformers - increase voltage • Fewer wraps around primary coil • More wraps around secondary coil.

Generating Electricity 1831: Michael Faraday discovers electromagnetic induction. – Electric current can be generated by moving a conducting wire through a magnetic field.

Today large generators move massive coils of wire rotating between powerful magnets to generate enough electricity to power entire cities.

1. DC Generator - is structurally the same as a DC motor. if electricity is passed through a DC generator, it will spin like a motor.

2. AC Generators • As the motor turns one side of the coil moves up between the magnets and the other side moves down. • Current is induced in the coil. • As the generator continues to rotate current is induced in the coil in the opposite direction, due to two slip rings. • This reversal of current every ½ rotation generates alternating current.

• Generator Animation

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. The slip rings conduct the alternating current to the circuit through the brushes.

Types of Generators: • Wind • Hydro-electric • Steam driven: nuclear, coal, geothermal and biomass.

• Now Do Check and Reflect P. 331#1 -4, 7 -10

3. 3 Measuring Energy Input and Output A. Power - the rate at which we use energy. Measured in Watts (W) 1 Watt = 1 J/sec. • Power is calculated by multiplying current x voltage P = IV

P =Ix. V I =P/V V=P/I P = power in watts (W) I = current in amperes (A) V = voltage in volts (V)

Example: An electric stove runs on 240 V and draws 30 A of current. How much power does it use?

Example: • An electric stove runs on 240 V and draws 30 A of current. How much power does it use? V = 240 V I = 30 A P=?

Example: • An electric stove runs on 240 V and draws 30 A of current. How much power does it use? V = 240 V I = 30 A P=? P = IV

Example: • An electric stove runs on 240 V and draws 30 A of current. How much power does it use? V = 240 V I = 30 A P=? P = IV = (30 A)(240 V) = 7200 W

What do you suppose it would cost to run each of these appliances for one hour? (A) This light bulb is designed to operate on a potential difference of 120 volts and will do work at the rate of 100 W. (B) The finishing sander does work at the rate of 1. 6 amp x 120 volts or 192 W. (C) The garden shredder does work at the rate of 8 amps x 120 volts, or 960 W.

B. Energy: The ability to do work. Measured in Joules (J). E = Input power x the time device operates E = Pt

E=Pxt P=E/t t =E/P E = energy in joules (J) P = power in watts (W) or (J/s) t = time in seconds (s)

Example A 800 W microwave runs for 3 minutes. How much energy does it use?

Example • A 800 W microwave runs for 3 minutes. How much energy does it use? E = Pt P= 800 W t= 3 min E= ?

Example • A 800 W microwave runs for 3 minutes. How much energy does it use? E = Pt P= 800 W t= 3 min x 60 s/min = 180 s E= ?

Example • A 800 W microwave runs for 3 minutes. How much energy does it use? E = Pt P= 800 W = (800 W)(180 s) t= 3 min x 60 s/min = 180 s = 144000 J E= ? or 144 KJ

Kilowatt Hours • Joules are a very small unit of measure. • A more common way to measure energy is to use kilojoules or kilowatt hours. • The formula for energy remains the same, but we use KW for power and hours for time. E = Pt J=Ws KJ = KW h

This meter measures the amount of electric work done in the circuits, usually over a time period of a month. The work is measured in k. Whr.

Energy Dissipation • Law of Conservation of Energy: Energy can not be created or destroyed, only transformed from one form to another. • However, the output energy of a device is almost always less than the input energy. Why?

• Some of the energy has dissipated as heat or other forms of unusable energy (like sound). • No mechanical system is 100% percent efficient. Therefore, the output energy will always be less than the input energy. This is due to friction.

C. Efficiency Calculations % efficiency = output energy (J) x 100 input energy (J)

Example: • A typical gas powered SUV produces 81 KJ of useful output energy for every 675 KJ of input energy (supplied by the fuel). Calculate the efficiency of the SUV.

Example: • A typical gas powered SUV produces 81 KJ of useful output energy for every 675 KJ of input energy (supplied by the fuel). Calculate the efficiency of the SUV. Easiest way to solve is to use a ratio Eout = 81 J = ____ Ein 675 J 100

Example: • A typical gas powered SUV produces 81 KJ of useful output energy for every 675 KJ of input energy (supplied by the fuel). Calculate the efficiency of the SUV. Easiest way is to use a ratio Eout = 81 J = 0. 12 X 100 Ein 675 J 12% efficient

Comparing Efficiencies • Florescent lights are about 4 x more efficient than incandescent lights. • Arc-discharge lights (streetlights) are even more efficient. • Hybrid gasoline-electric vehicles are more efficient than gaspowered vehicles.

• Do Check and Reflect P. 338 # 1 -9

3. 4 Reducing the Energy Wasted by Devices that 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 heater 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.

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. eg. Bearings, lubricants Insulating a device from heat loss is also another practical way to increase efficiency. Using capacitors (formerly condensers) in electrical circuits is also another way to increase efficiency.

• Do Worksheet 3. 4 • Check and Reflect P. 342 #4, 5, 6 • and Section Review P. 343