Www.energyquest.ca.gov/story/ind ex.html Renewable Energy Resources and Environment Chapter 9- The Energy Story.

www.energyquest.ca.gov/story/index.html

Renewable Energy Resources and Environment

Chapter 9- The Energy Story


Section 10.1 What is Energy

• Energy causes things to happen around us. For example, look out the window. During the day, the sun gives out light and heat energy. At night, street lamps use electrical energy to light our way.

• When a car drives by, its being powered by gasoline, a type of stored energy.

• The food we eat contains energy. We use that energy to work and play.

• We learned the definition of energy in the introduction.


• ENERGY IS THE ABILITY TO DO WORK.

• Energy can be found in a number of different forms. It can be chemical energy, electrical energy, heat (thermal) energy, light (radiant) energy, mechanical energy, and nuclear energy.


Stored and Moving Energy

• Energy makes everything happen and can be divided into two types:– Stored energy is called potential energy.– Moving energy is called kinetic energy.

• For example, when you push a pencil from the edge of the desk, the moving pencil uses kinetic energy and when you pick up the pencil and put it back on the desk, you use your own energy to lift and move the pencil. Moving it higher than the floor adds energy to it. As it rests on the desk, the pencil has potential energy. The higher it is, the further it could fall. That means the pencil has more potential energy.


How Do We Measure Energy?

• Energy is measured in many ways.• One of the basic measuring blocks is called a Btu (British

thermal unit).• Btu is the amount of heat energy it takes to raise the

temperature of one pound of water by one degree Fahrenheit, at sea level.

• Examples:– One Btu equals about one blue-tip kitchen match.– One thousand Btus roughly equals one average candy bar or

4/5 of a peanut butter and jelly sandwich.– It takes about 2,000 Btus to make a pot of coffee.


… How Do We Measure Energy?

• Energy can also be measured in joules. • A thousand joules equals to a Btu. (1,000 joules = 1 Btu)

• The term “joule” is named after an English scientist James Prescott Joule. He discovered that heat is a type of energy.

• One joule is the amount of energy needed to lift something weighing one pound to a height of nine inches.

• Around the world, scientists measure energy in joules rather than Btus.


… How Do We Measure Energy?

• Like in the metric system, you can have kilojoules – “kilo” means 1,000.

• 1,000 joules=1 kilojoule=1 Btu• For example, a piece of buttered toast contains about

315 kilojoules (315,000 joules) of energy. With that energy you could:

• Jog for 6 minutes• Bicycle for 10 minutes• Walk briskly for 15 minutes• Sleep for 1-1/2 hours• Run a car for 7 seconds at 80 Km/h• Light a 60-watt light bulb for 1-1/2 hours• Or lift a sack of sugar from floor to counter 21,000 times!


Changing Energy

• Energy can be transformed into another kind of energy. But it cannot be created and it cannot be destroyed. Energy has always existed in one form or another.

• Here are some changes in energy from one form to another:– Stored energy in a flashlight’s batteries becomes light energy

when the flashlight is turned on.– Food is stored energy. It is stored as a chemical with potential

energy. When your body uses the stored energy to do work, it becomes kinetic energy.

– If you overeat, the energy in food is not “burned” but is stored as potential energy in fat cells.


… Changing Energy

• …– When you talk on the phone, your voice is transformed into

electrical energy, which passes over wires (or is transmitted through the air). The phone on the other end changes the electrical energy into sound energy through the speaker.

– A car uses stored chemical energy in gasoline to move. The engine changes the chemical energy into heat and kinetic energy to power the car.

– A toaster changes electrical energy into heat and light energy.– A television changed electrical energy into light and sound

energy.


Heat Energy

• Heat is a form of energy. We use it for a lot of things, like warming our homes and cooking out food.

• Heat energy moves in three ways:1. Conductor

2. Convection

3. Radiation


Conduction

• Conduction occurs when energy is passed directly from one item to another. If you stirred a pan of soup on the stove with a metal spoon, the spoon will heat up.

• The heat is being conducted from the hot area of he soup to the colder area of the spoon.

• Metals are excellent conductors of heat energy. Woods or plastics are not. These “bad” conductors are called insulators.

• That is why a pan is usually made of metal while its handle is made of a strong plastic.


Convection

• Convection is the movement of gasses or liquids from a cooler spot to a warmer spot.

• For example:– If a soup pan is made of glass, we could see the movement of

convection currents in the pan. The warmer soup moves up from the bottom of the pan (heated are) to the top where it is cooler. The cooler soup then moves to take the warmer soup’s place. The movement is in a circular pattern within the pan.


… Convection

• The wind we feel outside is often the result of convection currents.

• You can understand this by the winds you feel near an ocean. Warm air is lighter than cold air and so it rises. During the daytime, cool air over water moves to replace the air rising up as the land warms the air over it.

During the nighttime, the directions change – the surface of the water is sometimes warmer and the land is cooler.


• Examples of convection


Radiation

• Radiation is the final form of movement of heat energy. The sun’s light and heat cannot reach us by conduction or convection because space is almost completely empty. There is nothing to transfer the energy from the sun to the earth.

• The sun’s rays travel in straight lines called heat rays. When it moves that way, its called radiation.


… Radiation

• When sunlight hits the earth, its radiation is absorbed or reflected. Darker surfaces absorb more of the radiation and lighter surfaces reflect the radiation.

• So you would be cooler if you wear light or white clothes in the summer.



Section 10.2 - What is Electricity?

• Electricity figures everywhere in our lives. Electricity lights up our homes, cooks our food, powers our computers, television sets, and other electronic devices. Electricity from batteries keeps our cars running and makes our flashlights shine in the dark.

• You’ll be amazed at how many things we use each and every day that depends on electricity.

• But what is electricity? Where does it come from? How does it work?

• Before we understand all these, we need to know about atoms and their structure.


… What is Electricity?

• All matter is made up of atoms, and atoms are made up of smaller particles. The three main particles making up an atom are the proton, the neutron and the electron.

• Electrons spin around the center, or nucleus, of atoms, in the same way the moon spins around the earth. The nucleus is made up of neutrons and protons.

• Electrons contain a negative charge, protons a positive charge. Neutrons are neutral – they have neither a positive nor a negative charge.




• There are many different kinds of atoms, one for each type of element. An atom is a single part that makes up an element. There are 118 different known elements that make up everything! Some elements like oxygen we breathe are essential to life.

• Each atom has a specific number of electrons, protons and neutrons. But no matter how many particles an atom has, the number of electrons usually needs to be the same as the number of protons. If the numbers are same, the atom is called balanced, and it is very stable.



• For example, if an atom had six protons, it should also have six electrons. The element with six protons are six electrons is called carbon.

• Carbon is found in abundance in the sun, starts, comets, atmospheres of most planets, and the food we eat. Coal is made of carbon; so are diamonds.

• Some kinds of atoms have loosely attached electrons. An atom that loses electrons has more protons than electrons and is positively charged.



• An atom that gains electrons has more negative particles and is negatively charge. A “charged” atom is called an “ion”.

• Electrons can be made to move from one atom to another. When those electrons move between the atoms, a current of electricity is created.

• The electrons move from one atom to another in a “flow”. One electron is attached and another electron is lost.

• The charge is passed from atom to atom when electricity is “passed”.




• Scientists and engineers have learned many ways to move electrons off of atoms. That means that when you add up the electrons and protons, you would wind up with one more proton instead of being balanced.

• Since all atoms want to be balanced, the atom that has been “unbalanced” will look for a free electron to fill the place of the missing one. We say that this unbalanced atom has a “positive charge” (+) because it has too many protons.

• While the free electrons moves around waiting for an unbalanced atom to give it a home. The free electron charge is negative, and has no proton to balance it out, so we say it has a “negative charge” (-).



• So what do positive and negative charges have to do with electricity?

• Scientists and engineers have found several ways to create large numbers of positive atoms and free negative electrons. Since positive atoms want negative electrons so they can be balanced, they have a strong attraction for the electrons.

• The electrons also want to be part of a balanced atom, so they have a strong attraction to the positive atoms. So, the positive attracts the negative to balance out.



• The more positive atoms or negative electrons you have, the stronger the attraction for the other. Since we have both positive and negative charged groups attracted to each other, we call the total attraction “charge”.

• When electrons move among the atoms of matter, a current of electricity is created. This is what happens in a piece of wire. The electrons are passed from atom to atom, creating an electrical current from one end to other.



• Electricity is conducted through some things better than others do. Its resistance measures how well something conducts electricity. Some things hold their electrons very tightly.

• Electrons do not move through them very well. These things are called “insulators”. Rubber, plastic, cloth, glass and dry air are good insulators and have very high resistance.

• Other materials have some loosely held electrons, which move through them very easily. These are called “conductors”. Most metals like copper, aluminium or steel are good conductors.


Section 10.3 – Resistance and Static Electricity

• As we have learned, some kinds of atoms contain loosely attached electrons. Electrons can be made to move easily from one atom to another.

• When those electrons move among the atoms of matter, a current of electricity is created.

• Take a piece of wire. The electrons are passed from atom to atom, creating an electrical current from one end to the other.

• Electrons are very small. A single copper penny contains more than 10,000,000,000,000,000,000,000 (1 x 1022) electrons.


… Resistance and Static Electricity

• Electricity “flows” or moves through some things better than others do. The measurement of how well something conducts electricity is called its resistance.

• Resistance in wire depends on how thick and how long it is, and what it’s made of. The thickness of wire is called its guage. The smaller the guage, the bigger the wire. Some of the largest thicknesses of regular wire is guage 1.



• Different types of metal are used in making wire. You can have copper wire, aluminum wire, even steel wire. Each of these metals has a different resistance; how well the metal conducts electricity.

• The lower the resistance of a wire, the better it conducts electricity.

• Copper is used in many wires because it has a lower resistance than many other metals.

• For example the wires inside your walls and lamps are copper.



• A piece of metal can be made to act like a heater. When an electrical current occurs, the resistance causes friction and the friction causes heat.

• The higher the resistance, the hotter it can get. So, a coiled wire high in resistance, like the wire in a hair dryer, can be very hot.



• Some things conduct electricity very poorly. These are called insulators.

• Rubber is a good insulator, and that’s why rubber is used to cover wires in an electric cord.

• Glass is another good insulator. If you look at the end of a power line, you’ll see that it is attached to some bumpy looking things. These are glass insulators. They keep the metal of the wires from touching the metal of the towers.


Static Electricity

• Another type of electrical energy is static electricity. Unlike current electricity that moves, static electricity stays in one place.

• Try this experiment explained in the next slide.


… Static Electricity

• Rub a balloon filled with air on a wool sweater or on your hair. Then hold it up to a wall. The balloon will stay there by itself.

• Tie strings to the ends of two balloons. Now rub the two balloons together, hold them by strings at the end and put them next to each other. They’ll move apart.

• Rubbing the balloons gives them static electricity. When you rub the balloon it picks up extra electrons from the sweater or your hair and becomes slightly negatively charged.




• The negative charges in the single balloon are attracted to the positive charges in the wall.

• The two balloons hanging by the strings both have negative charges. Negative charges always repel negative charges and positive always repel negative charges. So the two balloons negative charges “push” each other apart.



• Static electricity can also give you a shock.

• If you walk across a carpet, shuffling your feet and touching something made of metal, a spark can jump between you and the metal object.

• Shuffling your feet picks up additional electrons spread over your body. When you touch a metal object or something with positive charge, the electricity jumps across the small gap of your fingers and the object.

• If you walk across the carpet and touch a computer case, you can damage the computer.



• One other type of static electricity is very spectacular. It’s the lightning in a thunder and lightning storm.

• Clouds become negatively charged as ice crystals inside the clouds rub against each other. Meanwhile, on the ground, the positive charge increases. The clouds gets so highly charged that the electrons jump from the ground to the cloud, or from one cloud to another cloud.

• This causes a huge spark of static electricity in the sky that we call lightning.


• Example of static electricity


But What Is Static Electricity?

• Around 600 BCE greeks noticed that when rubbing “electron” against a piece of fur, the amber would start attracting particles of dust, feathers and straw.

• Then in 1600, Dr. William Gilbert investigated the reaction of magnets and amber and discovered that other objects can be made “electric” and that electricity repeled the same kind and attracts the opposite kind of electricity.

• In 1747, Benjamin Franklin and William Watson supported that all materials posses some kind of electrical “fluid” and supported the idea that rubbing moves this unseen fluid from one thing to another, electrifying both.


… But What Is Static Electricity?

• Franklin defines the fluid as positive and the lack of fluid as negative. Therefore, according to Franklin, the direction of flow was from positive to negative. Today, we know that the opposite is true.

• This is how, scientists theories developed.

• Instead of electricity being fluid, it is the movement of the charged particles between objects… the two objects are really exchanging electrons.


Section 10.4 -- Circuits

• Electrons with a negative charge, cannot “jump” through the air to a positively charged atom. They have to wait until there is a link or bridge between the negative area and the positive area. We usually call this bridge a “circuit”.

• When a bridge is created, the electrons begin to move quickly. Depending on the resistance of the material making up the bridge, they try to get across as fast as they can. If you’re not careful, too many electrons can go across at one time and destroy the “bridge” or the circuit, in the process.


… Circuits

• We can limit the number of electrons crossing over the “circuit”, by letting only a certain number through at a time. And we can make electricity do something for us while they are on their way.

• For example, we can “make” the electrons “heat” a filament in a bulb, causing it to glow and give off light.

• When we limit the number of electrons that can cross over our circuit, we say we are giving it “resistance”. We “resist” letting all the electrons through. This works like a tollbooth on a freeway bridge. Copper wire is just one type of bridge we use in circuits.


… Circuits

• Before electrons can move far, however, they can collide with one of the atoms along the way. This slows them down or even reverses their direction. As a result, they lose energy to the atoms. This energy appears as heat, and the scattering is a resistance to the current.

• Current refers to the movement of charges. In an electrical circuit – electrons move from the negative pole to the positive. If you connected the positive pole of an electrical source to the negative pole, you create a circuit.


… Circuits

• This charge changes into electrical energy when the poles are connected in a circuit – similar to connecting the two poles on opposite ends of a battery.

• Along the circuit you can have a light bulb and an on-off switch. The light bulb changes the electrical energy into light and heat energy.



Circuit Experiment

• You can build a very basic electrical circuit and find out what happens when a circuit is “open” compared with when it’s “closed”.

• Here’s what you need:– Penlight bulb– Flashlight battery– Two 6" pieces of insulated wire (any kind will work)– Tape to keep the wire on the end of the battery– A small piece of thin flat metal to make a “switch”– Small block of wood


Here’s What To Do!

1. Make a switch:• Take the block of wood and stick one thumb tack in• Push the other thumbtack through the thin piece of flat metal• Push the thumb tack into the wood so that the piece of metal can

touch the other thumb tack (see picture)

2. Connect the first piece of wire to a thumbtack on the switch.

3. Place the light bulb in the center of this wire piece.4. Tape the end of the first piece of wire to one end of the

battery.5. Tape your second piece of wire to the opposite end of the

battery.6. Attach the end of your second piece of wire to the

remaining thumbtack on the switch.

You’ve created an electrical circuit!!!



… Circuit Experiment

• When you press the switch connecting the two thumbtacks, your circuit is “closed” and your current flows – turning your light bulb on.

• When your switch is up, your circuit is ”open” and your current can not flow – turning your light bulb off.


… Circuits

• The number of electrons we are willing to let across the circuit at one time is called “current”.

• We measure current using amperes, or “Amps”.

• For example:– One AMP is defined as 625,000,000,000,000,000,000 (6.25 x

1018) electrons moving across your circuit every second.


… Circuits

• The amount of charge between the sides of the circuit is called “voltage”. We measure Voltage in Volts.

• The word Volt was named after a scientist, Alexander Volta, who built the world’s first battery.

• One volt is defined as the amount of electrical charge needed to make one Coulomb(625,000,000,000,000,000,000

electrons) do one specific amount of work – which is labelled one joule.


… Circuits

• Voltage, Current and Resistance are very important to circuits. If either voltage or current is too big you could break the circuit. But if either is too small, the circuit will not be able to work enough to be useful to us.

• In the same way, if the resistance is too big none of the electrons would be able to get through at all, but if it were too small, they would rush through all at one breaking the circuit on their way.


Parallel Circuits!

• When we have only one circuit that electrons can go through to get to the other side we call it a “series circuit”.

• If we were to set up another circuit next to the first one, we would have two circuits between the charges. We call these “parallel circuits” because they run parallel to each other.

• You can have as many parallel circuits as you want. Parallel circuits share the same voltage, but they allow more paths for the electricity to go over. This means that the total number of electrons that can get across (the current) can increase, without breaking either circuit.



Electric Motors

• An electric motor uses circuits wound round and round. These wound circuits are suspended between magnets.

• A motor works through electromagnetism. It has a coiled up wire (the circuit) that sits between the north and south poles of a magnet.

• When current flows through the coiled circuit, another magnetic field is produced.



… Electric Motors

• The north pole of the fixed magnet attracts the south pole of the coiled wire.

• The two north poles push away, or repulse, each other. The motor is set up in a way the attraction and repulsion spins the center section with the coiled wire.


Section 10.5 – Stored Energy and Batteries

• Energy cannot be created or destroyed, but it can be saved in various forms. One way to store it is in the form of chemical energy in a battery.

• When connected in a circuit, a battery can produce electricity.

• If you look at a battery it has two ends – a positive terminal and a negative terminal.

• If you connect the two terminals with wire, a circuit is formed. Electrons will flow through the wire and a current of electricity will be produced.


• Inside the battery, a reaction between the chemicals takes place. But reaction takes place only if there is a flow of electrons.

• Batteries can be stored for a long time and still work because the chemical process doesn’t start until the electrons flows from the negative terminals to the positive terminals through a circuit.


How The Chemical Reaction Takes Place In A Battery

• A very simple modern battery is a zinc-carbon battery, called the carbon battery for short.

• This battery contains acidic material within and a rod of zinc down the center.

• When zinc is inserted into an acid, the acid begins to eat away the zinc, releasing hydrogen gas and heat energy. The acid molecules break up into its components: usually hydrogen and other atoms.


• The process releases electrons from the zinc atoms that combine with hydrogen ions in the acid and to create the hydrogen gas.

• If a rod of carbon is inserted into the acid, the acid does nothing to it. But if you connect the carbon rod to the zinc rod with a wire, creating a circuit, electrons will begin to flow through the wire and combine with hydrogen on the carbon rods.

• This still releases some hydrogen gas but it makes less heat. Some of that heat energy is the energy that is flowing through the circuit.


• The energy in that circuit can now light a light bulb in a flashlight or turn a small motor. Depending on the size of the battery, it can even start an automobile.

• Eventually, the zinc rod is completely dissolved by the acid in the battery, and the battery can no longer be used.


Different Types of Batteries

• Different types of batteries use different types of chemicals and chemical reactions. Some of the more common types of batteries are:

– Alkaline battery: used in Duracell” and Energizer” and other alkaline batteries. The electrodes are zinc and manganese-oxide. The electrolyte is an alkaline paste.

– Lead-acid battery: these are used in automobiles. The electrodes are made of lead and lead-oxide with a strong acid as the electolyte.


Different Types of Batteries

– Lithium battery: these batteries are used in cameras for the flash bulb. They are made with lithium, lithium-iodide. They can supply surges of electricity for the flash.

– Lithium-ion battery: these batteries are found in laptop computers, call phones and other high-use portable equipment.

– Nickel-cadmium or NiCad battery: the electrodes are nickel-hydroxide and cadmium. The electrolyte is potassium-hyroxide.

– Zinc-carbon battery or standard carbon battery: zinc and carbon are used in all regular or standard AA, C and D dry-cell batteries. The electrodes are made of zinc and carbon, with a paste of acidic materials between them serving as the electolyte.


Food - Another Method of Storing Energy

• Batteries store energy in a chemical process, but there are other ways of storing energy. Consider the “food chain” on our planet.

• Plants, like grass in a meadow, convert the sun’s energy through photosynthesis into stored chemical energy. This energy is stored in the plant cells is used by the plant to grow, repair itself and reproduce itself.


• Cows and other animals eat the energy stored in the grass or grain and convert that energy into stored energy in their bodies.

• When we eat meat or other animal products, we in turn, store that energy in our own bodies. We use the stored energy to walk, run, ride a bike or even read a page on the internet.

Www.energyquest.ca.gov/story/ind ex.html Renewable Energy Resources and Environment Chapter 9- The Energy Story.

Documents