Ch 20 — Electricity I Electric Charge ª

Ch. 20 - Electricity I. Electric Charge ª Electricity ª Static Electricity ª Conductors ª Insulators ª Electroscope

A. Electricity ª Everything in the world is made up of atoms. Each atom has smaller parts in it. One of those parts is called electrons. Electrons can move from atom to atom. When an electron moves to a different atom, it causes another electron to have to move. When electrons move quickly from one atom to another is it called Electricity!

A. Electricity ª When you talk to your friends on the telephone, the microphone inside of the phone’s handset changes your sound waves into electric signals. The light shines throughout your homes when you flip a switch. And if you stump your toe, your nerves send signals between your brain and muscles. ª All of these everyday occurrences are powered by electrical pulses. A charge is a measure of the extra positive or negative particles that an object has. ª The only reason that we are able to use electricity in our modern world is that it is possible to separate positive and negative charges from each other.

A. Electricity 2 rules of electric charge: 1. Like charges repel. 2. Opposite charges attract

B. Static Electricity ª The study of the behavior of electric charges ª How the electric charge is transferred between objects: w by friction, conduction, and induction.

C. Transferring Charge Friction Conduction Induction Transfer of charge by rubbing two different materials together. Transfer of charge when Transfer of charge two objects come into without direct contact with each other. Rubbing a balloon in your hair. Touching a metal Being struck by sphere that has been lightning b/c you are charged b a Van de standing near a tree. Graff generator.

C. Transferring Charge Friction Example 1 Example 2

C. Transferring Charge Conduction Transfer by direct contact

C. Transferring Charge Conduction ª Conductor w material that allows electrons to move through it easily w e- are loosely held w ex: metals like copper and silver

C. Transferring Charge Conduction ª Insulator w material that doesn’t allow electrons to move through it easily w e- are tightly held w ex: plastic, wood, rubber, glass

C. Transferring Charge Induction

Ch. 20 - Electricity II. Electric Current ª Circuit ª Electric Current ª Resistance ª Ohm’s Law

B. Electric Current ª Current w flow of electrons through a conductor w depends on # of e- passing a point in a given time w measured in amperes (A)

B. Electric Current The continuous flow of electric charge is an electric current. There are 2 types of electric current: direct current and alternating current. Flow of charges in only one direction Flow of charges that regularly reverses direction

D. Resistance ª Resistance w opposes the flow of electrons w electrical energy is converted to thermal energy & light w measured in ohms ( ) Copper - low resistance Tungsten - high resistance

D. Resistance ª Resistance depends on… w the conductor w wire thickness • less resistance in thicker wires w wire length • less resistance in shorter wires w temp - less resistance at low temps

D. Resistance Ohm’s Law ª Most of the electrical appliances that you use in your homes The difference in their current is each day are designed for 120 because of their resistance. Volts (V). In other words, 40 W light bulbs have a ª Light bulbs however are sold in greater resistance (less current than several varieties, from dim 40 the 100 W bulbs) and therefore give off Watt light bulbs to bright 100 less light. Watt light bulbs. Therefore greater resistance = less ª These bulbs shine differently current because they have different amounts of current in them.

D. Resistance Ohm’s Law ª You have probably noticed that electrical devices such as video games or radios become warm after they have been on for a long amount of time. ª As the electrons collide, with the atoms of the material, some of their kinetic energy transfers. ª This transfer of energy causes the atoms to vibrate, and then the material warms up. ª As the electrons are slowed by a resistor, energy is lost in the form of heat. ª This means that current, resistance and voltage must be linked.

D. Resistance Ohm’s Law Did you know that resistance depends on the material used as well as the material’s length and temperature? ª Longer pieces of material have greater resistance (less current) than shorter pieces.

E. Calculating Resistance Ohm’s Law ª Ohm’s Law - The SI unit of resistance is the ohm, Ω, V: potential difference (V) V=I×R I: current (A) R: resistance ( ) • Voltage increases when current increases. • Voltage decreases when resistance increases.

E. Calculating Resistance Ohm’s Law ª A lightbulb with a resistance of 160 is plugged into a 120 -V outlet. What is the current flowing through the bulb? GIVEN: WORK: R = 160 V = 120 V I = ? I = V ÷ R I = (120 V) ÷ (160 ) I = 0. 75 A I V R

Homework Practicing Ohm’s Law

Ch. 21 - Electricity III. Electrical Circuits ª Circuit components ª Series circuits ª Parallel circuits ª Household circuits

A. Circuit ª Circuit w closed path through which electrons can flow

Electrical Circuits ª If you’ve ever seen a house being built, you know that wires hidden inside the walls connect to every electrical outlet and to every light switch. ª The steady flow of electricity is called an electric current. ª A current will move along a wire or a path called a circuit. Circuit means to “go around. ” ª There are 2 types of circuits: series circuit and parallel circuit.

A. Circuit Components A - battery B - switch C - light bulb D - resistor

Circuit Symbols

B. Series Circuits ª Series Circuit w current travels in a single path • one break stops the flow of current w current is the same throughout circuit • lights are equal brightness w each device receives a fraction of the total voltage • get dimmer as lights are added

C. Parallel Circuits ª Parallel Circuits w current travels in multiple paths • one break doesn’t stop flow w current varies in different branches • takes path of least resistance • “bigger” light would be dimmer w each device receives the total voltage • no change when lights are added

Series Circuit vs. Parallel Circuit ª A series circuit is a circuit that has only one path for the current. ª A parallel circuit has two or more paths for current to travel. Series Circuit Parallel Circuit Old Christmas Lights were once Lights in our homes are wired in series. If one bulb went out, parallel circuit. That is why we are to they all went out. have lights on in one room, but off in another.

Series Circuit vs. Parallel Circuits 1. Has two or more paths for Series 1. Has a single loop for electrons Parallel electrons to flow down to travel round 2. Current is shared between the branches 2. Components are connected one after another 3. Current has to travel through all components

D. Household Circuits ª Combination of parallel circuits w too many devices can cause wires to overheat ª Safety Features: w fuse - metal melts, breaking circuit w circuit breaker - bimetallic strip bends when hot, breaking circuit

Ch. 21 - Magnetism I. Characteristics of Magnets w Magnetism w Magnetic poles w Magnetic field w Magnetic domain

A. Magnetism ª Magnetism w force of attraction or repulsion between unlike or like poles w due to the arrangement of electrons w closely related to electricity w Magnetism is the force of attraction or repulsion of a magnetic material due to the arrangement of its atoms, particularly its electrons.

A. Magnetism: The History of Magnets ª Magnets have been known for centuries. The Chinese and Greeks knew about the “magical” properties of magnets. The ancient Greeks used a stone substance called “magnetite. ” They discovered that the stone always pointed in the same direction. Later, stones of magnetite called “lodestones” were used in navigation.

B. Magnetic Poles ª The ends of a magnet are where the magnetic effect is the strongest. These are called “poles. ” Each magnet has w 2 poles – 1 north, 1 south. ª If you cut a magnet in half, you get two magnets. Like Poles: Repel Opposite poles: Attract

B. Magnetic Poles ª Magnetic Poles w like poles repel w unlike poles attract w a broken magnet creates new poles

C. Magnetic Field ª Magnetic Field w area around a magnet where magnetic forces act w field lines show direction of field (N S)

Permanent Magnets vs. Temporary Magnets ª Some magnets occur in nature. These magnets are called natural magnets. Natural magnets maintain their magnetic properties and therefore are permanent magnets. (ex. lodestone). ª Some materials that are not natural magnets are easy to magnetize (ex. Iron). A material that is easily magnetized tends to lose its magnetism quickly, and is called a temporary magnet.

Permanent Magnets vs. Temporary Magnets ª An electric current passing through a wire causes a magnetic field. ª An electromagnet is a temporary magnet made by wrapping a current-carrying wire around an iron core. ª The center of an electromagnet is called the core, and it is often made of iron. ª As long as current is flowing, an electromagnet has a magnetic field. ª When current is turned off, there is no longer a magnetic field.

Ch. 21 - Magnetism II. Uses of Magnetic Fields w Electromagnet w Speaker w Motor

A. Electromagnet ª Electromagnet w strong, temporary magnet formed when current is passed through a coil of wire surrounding an iron core w acts like a bar magnet when current is on

A. Electromagnet ª There are two ways to make an electromagnet stronger: 1. increasing the number of coils 2. increasing the amount of current ª Electromagnets are useful because they can be turned on and off. Electromagnets have many important uses: w ex. radios, telephones, computers

B. Speaker ª Speaker w electrical energy mechanical energy w wire coil moves back & forth as its magnetic field interacts with the field of a fixed magnet w forced vibration causes the cone to move sound

C. Motor ª Motor w electrical energy mechanical energy w electromagnet rotates between the poles of a fixed magnet w commutator reverses the poles of the e’magnet

C. Motor assembled motor brushes & wires to battery armature & commutator field magnet

Ch. 22 - Magnetism III. Producing Electric Current (p. 633 -639) w Electromagnetic Induction w Electric Generator w DC & AC w Transformer

A. Electromagnetic Induction ª Electromagnetic Induction w producing a current by moving a wire through a magnetic field w some microphones work just like minispeakers in reverse w sound waves cause coil to move current Coil Dynamic Microphone

B. Electric Generator ª Electric Generator w mechanical energy electrical energy w armature is rotated between magnet poles w magnetic field induces a current in the wire coil GENERATOR MOTOR

B. Electric Generator ª Hydroelectric Dam w PE of lake water is converted to KE w mechanical KE turns the generator shaft which creates electrical energy

C. DC & AC ª Direct Current (DC) w current flows in one direction w dry cells Ø Alternating Current (AC) w current reverses its direction at regular intervals w electrical outlets

D. Transformer ª Transformer w increases or decreases AC voltage w primary coil AC produces a magnetic field that induces AC in the secondary coil w voltage ratio = ratio of turns in each coil

D. Transformer ª Step-up Transformer w increases the voltage w more turns w power plants Ø Step-down Transformer w decreases the voltage w fewer turns w household appliances (hairdryers, etc. )

Electric Motors vs. Generators ª An electric motor is a device that changes electrical energy into mechanical energy. ª An electric motor is made up of an electromagnet and a permanent magnet. ª So, what do windshield wipers, CD players, VCR's, blenders, ice makers, computers, and talking toys have in common? They all contain electric

Electric Motors vs. Generators ª A generator is a device that changes mechanical energy into electrical energy. ª Most of the energy we use every day comes from generators. ª Mechanical energy for many generators is supplied by turbines. ª A turbine is a large wheel that is turned by moving steam or water.

Electric Motors vs. Generators Motor or Generator?