ENERGY - CIRCUITS #D

Circuits

Electrons with a negative charge, can't "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 moving 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.

In Chapter 3, we learned about electrons and the attraction between positive and negative charges. We also learned that we can create a bridge called a "circuit" between the charges.

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 something like a tollbooth on a freeway bridge. Copper wire is just one type of bridge we use in 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.

Think of the bridge as a garden hose. The current of electricity is the water flowing in the hose and the water pressure is the voltage of a circuit. The diameter of the hose is the determining factor for the resistance.

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. 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

As a boy, Thomas Edisonbuilt a small laboratory in his cellar. His early experiments helped develop a very inquisitive mind. His whole life was spent thinking about how things work and dreaming up new inventions. The light bulb and movie projector are just two of dozens of inventions.

You can build a very basic electrical circuit similar to what Edison may have crafted as a boy. And you can find out what happens when a current is "open" compared with when it's "closed."

Here's What You need:

1. Penlight bulb
2. Flashlight battery
3. Two 6" pieces of insulated wire (any kind will work)
4. Tape to keep the wire on the end of the battery
5. A small piece of thin flat metal to make a "switch"
6. Small block of wood

Here's What to Do

1. To 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.

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, just like Thomas Edison's may have done.

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".

One AMP is defined as 6,250,000,000,000,000,000 (6.25 x 1018) electrons moving across your circuit every second!

Since no one wants to remember such a big number, that big number is called a "coulomb," after the scientist Charles A Coulomb who helped discover what a current of electricity is.

The amount of charge between the sides of the circuit is called "voltage." We measure Voltage in Volts. The word volt is named after another scientist, Alexader Volta, who built the world's first battery.

You'll remember that back in Chapter 1, we defined energy as the "ability to do work."

Well, 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 a specific amount of work – which is labeled one joule.

Joule is also named after a scientist, James Prescott Joule. Do you remember him from Chapter 2?

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 though at all, but if it were too small, they would rush though all at once 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. (We send a 'thank you' to How Stuff Works Website for their electric motor graphic.)

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. 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 that attraction and repulsion spins the center section with the coiled wire.

ELECTRICITY - RESISTANCE & STATIC ELECTRICITY #C

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, very small. A single copper penny contains more than 10,000,000,000,000,000,000,000 (1x1022) electrons.

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 gauge. The smaller the gauge, the bigger the wire. Some of the largest thicknesses of regular wire is gauge 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. The wires in your walls, inside your lamps and elsewhere are usually 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...

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 strings both have negative charges. Negative charges always repel negative charges and positive always repels positive 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 doorknob or something with a positive charge the electricity jumps across the small gap from your fingers just before you touch the metal knob. If you walk across a 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 up against each other. Meanwhile, on the ground, the positive charge increases. The clouds get 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.

You can find out more about lightning at Web Weather for Kids -www.ucar.edu/40th/webweather/

 But What Is Static Electricity?

You'll remember from Chapter 2 that the word "electricity" came from the Greek words "elektor," for "beaming sun" and "elektron," both words describing amber. Amber is fossilized tree sap millions of years old and has hardened as hard as a stone.

Around 600 BCE (Before the Common Era) Greeks noticed a strange effect: When rubbing "elektron" against a piece of fur, the amber would start attracting particles of dust, feathers and straw. No one paid much attention to this "strange effect" until about 1600 when Dr. William Gilbert investigated the reactions of magnets and amber and discovered other objects can be made "electric."

Gilbert said that amber acquired what he called "resinous electricity" when rubbed with fur. Glass, however, when rubbed with silk, acquired what he termed "vitreous electricity."

He thought that electricity repeled the same kind and attracts the opposite kind of electricity. Gilbert and other scientists of that time thought that the friction actually created the electricity (their word for the electrical charge).

In 1747, Benjamin Franklin in America and William Watson in England both reached the same conclusion. They said all materials possess a single kind of electrical "fluid." They didn't really know anything about atoms and electrons, so they called how it behaved a "fluid."

They thought that this fluid can penetrate matter freely and couldn't be created or destroyed. The two men thought that the action of rubbing (like rubbing amber with fur) moves this unseen fluid from one thing to another, electrifying both.

Franklin defined 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. Electricity flows from negative to positive. Others took the idea even further saying this that two fluids are involved. They said items with the same fluid attract each other. And opposite types of fluid in objects will make them repel each other.

All of this was only partially right. This is how scientific theories develop. Someone thinks of why something occurs and then proposes an explanation. It can take centuries sometime to find the real truth. Instead of electricity being a fluid, it is the movement of the charged particles between the objects... the two objects are really exchanging electrons.

ELECTRICITY - WHAT IS ELECTRICITY? #B

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.

Here's something you can do to see the importance of electricity. Take a walk through your school, house or apartment and write down all the different appliances, devices and machines that use electricity. You'll be amazed at how many things we use each and every day that depend on electricity.

But what is electricity? Where does it come from? How does it work? Before we understand all that, we need to know a little bit about atoms and their structure.

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 every thing! 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 the same, the atom is called balanced, and it is very stable.

So, if an atom had six protons, it should also have six electrons. The element with six protons and six electrons is called carbon. Carbon is found in abundance in the sun, stars, 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.

This chain is similar to the fire fighter's bucket brigades in olden times. But instead of passing one bucket from the start of the line of people to the other end, each person would have a bucket of water to pour from one bucket to another. The result was a lot of spilled water and not enough water to douse the fire. It is a situation that's very similar to electricity passing along a wire and a circuit. 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.

Since it got kicked off, the free electron 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 that 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."

Energy also can be measured in joules. Joules sounds exactly like the word jewels, as in diamonds and emeralds. A thousand joules is equal to a British thermal unit.

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, just like in the picture.

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, aluminum or steel – are good conductors.

 Where Does the Word 'Electricity' Come From?

Electrons, electricity, electronic and other words that begin with "electr..." all originate from the Greek word "elektor," meaning "beaming sun." In Greek, "elektron" is the word for amber.

Amber is a very pretty goldish brown "stone" that sparkles orange and yellow in sunlight. Amber is actually fossilized tree sap! It's the stuff used in the movie "Jurassic Park." Millions of years ago insects got stuck in the tree sap. Small insects which had bitten the dinosaurs, had blood with DNA from the dinosaurs in the insect's bodies, which were now fossilized in the amber.

Ancient Greeks discovered that amber behaved oddly - like attracting feathers - when rubbed by fur or other objects. They didn't know what it was that caused this phenomenon. But the Greeks had discovered one of the first examples of static electricity (see Chapter 3).

The Latin word, electricus, means to "produce from amber by friction."

So, we get our English word electricity from Greek and Latin words that were about amber.

MAGNETS & ELECTRIC CURRENTS -VIDEO


MAGNETS & ELECTRIC CURRENTS - QUIZ

Complete the quiz
write your name, quiz name, & score on notebook paper & turn in.

ELECTRICITY - ENERGY - WHAT IS IT? #A

READ EACH MODULE LABELED BY  LETTERS, READ CAREFULLY.  

• THEN GO BACK & USE THE CLOZE TO HELP YOU LEARN SPECIFICS.  

Energy - What Is It?

Energy causes things to happen around us. 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, it is 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.

With a pencil, try this example to know the two types of energy.

Put the pencil at the edge of the desk and push it off to the floor. The moving pencil uses kinetic energy.

Now, pick up the pencil and put it back on the desk. You used 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. This stands for British thermal unit and was invented by, of course, the English.

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.

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.

Energy also can be measured in joules. Joules sounds exactly like the word jewels, as in diamonds and emeralds. A thousand joules is equal to a British thermal unit.

1,000 joules = 1 Btu

So, it would take 2 million joules to make a pot of coffee.

The term "joule" is named after an English scientist James Prescott Joule who lived from 1818 to 1889. 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. So, if you lifted a five-pound sack of sugar from the floor to the top of a counter (27 inches), you would use about 15 joules of energy.

Around the world, scientists measure energy in joules rather than Btus. It's much like people around the world using the metric system of meters and kilograms, instead of the English system of feet and pounds.

Like in the metric system, you can have kilojoules — "kilo" means 1,000.

1,000 joules = 1 kilojoule = 1 Btu

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 kilometers per hour (about 50 miles per hour)
• Light a 60-watt light bulb for 1-1/2 hours
• Or lift that sack of sugar from the floor to the counter 21,000 times!

 Changing Energy

Energy can be transformed into another sort 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 that 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.

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. (If you look into the toaster, you'll see the glowing wires.)

A television changes electrical energy into light and sound energy.

 Food Energy

Energy changes form at each step in the food chain. Take an ear of corn as an example.

Sunlight is taken in by the leaves on the corn stalk and transformed through photosynthesis. The plant takes in sunlight and combines it with carbon dioxide from the air and water and minerals from the ground.

The plant grows tall and creates the ears of corn - its seeds. The energy of the sunlight is stored in the leaves and inside the corn kernels. The corn kernels are full of energy stored as sugars and starch. The corn is harvested and is fed to chickens and other animals. The chickens use the stored energy in the corn on the cob to grow and to move. Some energy is stored in the animal in its muscle tissue (protein) and in the fat.

The chicken reaches maturity, a farmer slaughters it and prepares it to be sold. It's transported to the grocery store. Your parents buy the chicken at the supermarket, bring it home and cook it (using energy).

You then eat the chicken's meat and fat and convert that stored energy into energy in your own body. Maybe you ate the chicken at a picnic. Then you went and played baseball. You're using the energy from that chicken to swing the bat, run the bases and throw the ball.

As your body uses the energy from the chicken, you breathe in oxygen and exhale carbon dioxide. That carbon dioxide is then used by other plants to grow.

So, it's a big circle!

Heat Energy 

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

Heat energy moves in three ways:

1. Conduction
2. Convection
3. Radiation

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 the soup to the colder area of spoon.

Metals are excellent conductors of heat energy. Wood or plastics are not. These "bad" conductors are called insulators. That's why a pan is usually made of metal while the handle is made of a strong plastic.

Convection is the movement of gases or liquids from a cooler spot to a warmer spot. 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 heated area at the bottom of the pan 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 (see picture above).

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.

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, it is called 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.

ENERGY - VIDEO

ENERGY TRANSFER & STORAGE

 - QUIZ 

• Complete the quiz
• write your name, quiz name, score on notebook paper & turn in