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Download Ch 17 Introduction to electricity
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CH 17 INTRODUCTION TO ELECTRICITY https://youtu.be/EJeAuQ7pkpc I. ELECTRICAL CHARGE AND STATIC ELECTRICITY A. ELECTRIC CHARGE 1. All matter is composed of atoms 2. Atoms have 1protons, 2electrons, & 3neutrons • Protons (+) • Electrons (-) • Neutrons (neutral or no charge) 3. Charged objects exert a force • Push or pull 4. Law of electrical charges= like charges repel (push away) & opposite charges attract 5. Protons (+) and electrons (-) attract each other or the atom would not stay together 6. Electrical force= force of attraction or repulsion on a charged particle that is die to an electric field • Depends on: 1 Amount of charge on each object (greater the charge= greater the force) 2 Distance between the charges (closer together= greater the force ) 7. Electrical field= the space around a charged object in which an electric force is exerted on another charged object • Other object will either be attracted or repelled STOP AND THINK…… • What are 2 types of charged particles in an atom? • Postive (+) Protons • Negative (-) Electrons B. CHARGE IT! 1. An object becomes POSITIVELY charged when it LOSES electrons • Losing negatives makes it more positive 2. An object becomes NEGATIVELY charged when it GAINS electrons • Gaining negatives makes it more negative 3. Three ways to charge an object: a. Friction= electrons are “wiped” from one object to another- rubbing a balloon on your head) b. Contact (Conduction)= electrons move from one object to another by touch https://youtu.be/T0J5q43MSw8 c. Induction= charges in an uncharged metal object are rearranged without direct contact with a charged object C. CONSERVATION OF CHARGES 1. Charges are not created or destroyed when you charge something by any of the 3 methods 2. The numbers of electrons & protons stay the same 3. Electrons are simply transferred from one object to the next D. DETECTING CHARGES 1. Electroscope= device that detects charges 2. Metal strips will hang straight when it is not charged 3. If a charged object touches the electroscope the strips will repel (move apart) 4. Does NOT show if the charged object is positive or negative LAB: CREATING AN ELECTROSCOPE TO DETECT CHARGES E. STATIC ELECTRICITY 1. “Static“ = not moving • Charges of the static electricity do not move away from the object they are in 2. Static electricity = the electric charge at rest on an object 3. Examples: static cling & charged balloons • Friction transfers the charge to the clothes or balloon and since the objects are insulators the charge stays after the friction ceases 3. Electric Discharge: the loss of electricity as charges move off an object https://youtu.be/yc2-363MIQs a. When you touch a door knob after shuffling your feet b. Lightening is caused by the large charge difference & rapid electrical discharge 4. Lightening rods on top of buildings are grounded so the charge goes into the Earth be absorbed • Lightening strike the highest point F. MOVING CHARGES 1. Electrical conductors= materials in which charges can move easily • Most metals 2. Electrical insulators= materials in which charges cannot move through easily • Electrons are held very tightly in these materials • Plastic, rubber, glass, wood & air 3. Semiconductors: special class of materials that conduct electric charge better than electrical insulators, but not as good as electrical conductors • Silicon used in computer chips https://www.youtube.com/watch?v=gixkpsrxk4Y&feature=youtu.be Electricity Review II. SIMPLE CIRCUITS A. PARTS OF A CIRCUIT 1. Electrical charges move in a path or circuit HTTPS://YOUTU.BE/VNNPLAKSQGU 2. Simple circuit contains: • Source of energy (battery) • At least one conductor (copper wire) • Resistor (light) • May contain a switch (closes and opens the circuit) 3. Flow of energy (electrons) go from the negative end of the battery to the positive end (likes repelopposites attract) 4. Energy in the circuit is called electrical energy 5. Some electrical energy changes to heat 6. Resistors= transform electrical energy to sound, light, thermal or mechanical energy • Light bulb • Buzzers STOP AND THINK 1. Into what forms of energy can resistors transform electrical energy? • Sound, light, thermal or mechanical energy 2. What is the role of insulators such as plastic, rubber, and cloth covering wires and other conductors in a circuit? • Insulators help keep the electric charges inside the pathway 3. Why aren’t batteries used to supply all power? • They could run out of energy B. CIRCUIT DIAGRAMS 1. Simple circuit diagram= map of a circuit in which the symbols represent each part of the circuit 2. Volt= measurement of electrical force provided by an energy source (V) 3. Ohm (Ω) unit of measurement of resistance 4. Current= measure of how much moves past a given spot charge (A) or amp STOP AND THINK 1. What unit measures resistance to electrical current? • Ohm (Ω) 2. What is the difference between volts and amps? • volts-= measure of electrical force provided by an energy source • Amp= measure how much current moves past a given spot each second in a circuit 3. Suppose a series circuit has three bulbs. One burns out. What will happen in the circuit? • The current will NOT be able to flow through and the bulbs will NOT light C. SERIES CIRCUITS 1. Current passes through all resistors 2. May have more than one resistor in the circuit 3. The more resistors on the circuit the lower the current is further down the circuit III. COMPLEX CIRCUITS HTTPS://WWW.MSNUCLEUS.ORG/MEMBERSHIP/SLIDESHOWS/ ELECTRICITY.HTML A. PARALLEL CIRCUITS 1. Parallel circuit has more than one branch or pathway • Each branch may hold several resistors where electrical energy can be put to work 2. Not all branches have to be on at the same time for the current to flow • Useful= you don’t have to have the light on in the kitchen to have the refrigerator running STOP AND THINK 1. Name two advantages of parallel circuits over series circuits • Parallel circuits have more than 1 branch and not all branches need to be on at the same time 2. What is an example of a parallel circuit in your home? • Lights in the room and the TV= many others 3. If one conductor on the computer chip is open, will the computer shut down? • No, the chip uses parallel circuits with millions of paths LESSON 4 MAGNETS & MAGNETISM A. PROPERTIES OF MAGNETS 1. Magnetic Force: the push or pull force resulting when two magnets are placed close to each other • Results from spinning electric charges in the magnets • Can act from a distance 2. Magnetic Poles: one of two ends of a magnet that have opposing magnetic qualities • North and south poles • Opposites attract & likes repel 3. Magnetic fields: area surrounding a magnet where magnetic forces can be detected • Strongest near the poles • Greater the distance from the poles the weaker the magnetic field Temporary Magnet Mini lab 1. Get a normal paperclip. What happens to the compass & the metal filings when the paperclip was put over it? 2. How will you magnetize the paperclip? 3. What happens to the compass and the metal filings after the paperclip is magnetized? 4. Draw the domains on the paperclip before and after magnetism B. WHAT CAUSES MAGNETISM? HTTPS: / / YOUTU. BE/ HFAOXDXZ5TM 1. The charged electrons in the atom of the magnetic object do NOT fully cancel each other out • Result is that these materials will have a magnetic field with 2 magnetic poles (north & south) • No matter how many times you cut the magnet, it will continue to have 2 poles 2. The formation of domains lined up makes a strong magnetic field • Domain= tiny magnetic areas formed by group of atoms in an object whose electrons do not fully cancel out • When the domains line up in the same direction they form a strong magnetic field together around the entire object C. TYPES OF MAGNETS 1. Ferromagnets= materials that can be turned into a magnet • Iron • Nickel • Cobalt 2. Electromagnets= iron core wrapped with electrical wire in which an electric current runs through the wire • When the electric current is turned on it is a strong magnet • When the electric is off the object the magnetic field stops 3. Temporary magnets= materials such as iron can be made into a magnet for a short period of time by using another magnet to line up the domains • Over time it will lose magnetism D. THE EARTH IS A GIANT MAGNET 1. The liquid outer core of the Earth is made of iron and nickel which creates a magnetic field when the Earth is in rotation • Stronger near the poles • The outer core is moving so the magnetic pole will change slightly overtime 2. The Earth has magnetic poles, but they are not exactly the geographic north and south pole • A compass has a “north seeking” pole and a “south seeking” pole HTTPS://YOUTU.BE/CZMH3BNHFHQ 3. Auroras= charged particles interacting with atoms in the atmosphere causing the atoms to emit visible lights. a. The type of particles will produce different colors Oxygen= greenish yellow or red Nitrogen= blue or deep red b. Aurora Borealis= Northern Hemisphere c. Aurora Australis= Southern Hemisphere LESSON 5 ELECTROMAGNETISM A. ELECTROMAGNETS HTTPS://YOUTU.BE/SMB1DSIJCUQ ELECTROMAGNET 1. Electromagnetism= results when electric currents and magnetic fields interact with each other 2. 1820 Danish professor Hans Christian Oersted noticed when he brought a compass close to the electric current the needle of a compass moved 3. Every electrical current produces a magnetic force 4. Solenoid= a coil of wire that carries an electric current producing a magnetic field 5. Electromagnets= wrapping a solenoid around an iron core • Combines the magnetic field of the solenoid with the magnetic field of the magnetized iron core 6. Electromagnets can be used to lift or move very heavy objects • Easy to turn on to lift and off to drop 7. To increase the strength of the electromagnet you can; a. Increase the current b. Increase the number of coils c. Add iron core d. Layer the coils http://study.com/a cademy/lesson/how-magnetic-fields-are-created.html 8. Galvanometer= device used that measures the strength and direction of an electric current in a wire 9. Electromagnets are used in MRI machines to take more detailed pictures of the inside of a person than xrays • Has to be super cooled to get the strongest magnetic field possible (reduces friction) STOP AND THINK 1. How was electromagnetism discovered? • Hans Christian Oersted noticed when he turned on an electric current the needle on the compass moved 2. Why is the ability to turn off an electromagnet advantageous? • There are times that it is not needed or to move heavy metal objects B. HOW DO MOTORS WORK? 1. Electric motor= changes electrical energy into mechanical energy • Can run on AC or DC current 2. Electric motors use electromagnets • A simple motor has an armature (coil or loop of wire) mounted between poles of a magnet • The armature (wire) is pushed and pulled • The commutator will change the direction of the current allowing the armature to make a complete rotation C. ELECTROMAGNETIC INDUCTION 1. 1830s Michael Faraday discovered that when a magnet was moved inside a metal coil it created an electric current 2. Electromagnetic induction= using a magnetic field to create an electric current D. CHANGING VOLTAGE 1. Transformers use induction to increase or decrease the voltage of alternating current • Iron “rings” with two coils of wire • The more coils the wire makes the higher the voltage and vice versa 2. Transformers on powerlines increase voltage to send it many miles away then decrease it to safe levels before sending it into a home DO THE MATH PAGE 463 • Get with a partner and do the calculation on the page by first multiplying the primary side volts by the secondary sides turns. Then divide the answer from above by the primary side turns. • SHOW YOUR RAITO SET UP • You may use a calculator for the math but you have to show the set up like the example in the book • One volunteer put it on the board E. ELECTRICAL GENERATORS HTTPS: / / YOUTU. BE/ 20VB6HLLQSG?T= 1M 44S 1. Electrical generators use induction to change mechanical energy into electrical energy • Generators are opposite of electrical motors 2. Generators induce electric current when a magnet moves in a coil of wire or when a wire moves between the poles of a magnet 3. Review: https://youtu.be/gixkpsrxk4Y ASSIGNMENT DUE MONDAY 1. Read 580-466 2. Answer questions 1-27 omitting #4, 10,& 17 3. ALSO pg 467 1-12 4. If you are quiet you may have partners for 1-27 5. NO PARTNERS for 1-12