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Electricity and Magnetism

Electricity and Magnetism. Protons have a ________ charge Electrons have a ________ charge Most atoms are neutral because_____ To become charge and atom will either _____ or _______ electrons Static electricity – the accumulation of excess electrical charges on an object.

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Electricity and Magnetism

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  1. Electricity and Magnetism Protons have a ________ charge Electrons have a ________ charge Most atoms are neutral because_____ To become charge and atom will either _____ or _______ electrons Static electricity – the accumulation of excess electrical charges on an object

  2. Law of conservation of charge-charge may be transferred but not created or destoyed. • Opposite charges _________ • Like charges __________ • A force surrounds every charge called an electromagnetic field. Forms the electromagnetic force that hold chemical bonds together as well as electricity

  3. Charges can act on each other even at a distance because any charge that is placed in an electric field will be pushed or pulled by the field • Electrons move easily through conductors (metal) • Electrons do not move easily through insulators like plastic, wood, rubber, and glass. • When two different objects are rubbed together (friction), electrons are transferred because of the contact area between them

  4. Conductor or Insulator • Silver, Copper, Aluminum, Iron, Silicon, Water, Glass, Styrofoam • Cork Penny Stick Rubberband • Nail Paperclip Nickel • Do any solutions allow electricity to move through them? (hint they have to be made up of charged particles)

  5. The higher on the list holds electrons loosely giving them away becoming more positively charged • TRIBOELECTRIC SERIES • your handyour hair Rub Glass rod with fur electrons movenylon from fur to rod, rod gets negative charge • woolfur Rub glass rod with silk , silk pulls electrons silk from rod and rod gets positive chargepapercottonhard rubberpolyesterpolyvinylchloride plastic

  6. 3 Methods to transfer charges • Charging by conduction, touching or rubbing Example rubbing shoes across carpet, pick up electrons becoming negatively charged

  7. Charging by induction, rearrangement of electrons on a neutrally charged object by a nearby charged object Example negatively charged balloon near sleeve causes an area of your sleeve to become positively charged

  8. Static discharge- a transfer of charge through the air between two objects because of the build up of static electricity Example-lightening Grounding- use of a conductor to conduct an electric charge into the ground

  9. Electroscope • http://www.shep.net/resources/curricular/physics/P30/Unit2/electroscope.html

  10. Electric Current (I) • Flow of electrons through conductor that is ductile (wire) • Current is measured in AMPERES (A) (6.281x1018 electrons per second so amperes are a _______) • CHARGES ALWAYS FLOW FROM HIGH VOLTAGE TO LOW VOLTAGE (no voltage difference, no flow) • Voltage is potential energy • Battery or wall sockets supply the voltage difference • Circuit-path electrons take • Circuit MUST BE CLOSED for electrons to flow

  11. Resistance • Tendency for a material to oppose the flow of electrons changing electrical energy into thermal energy and light • Measured in Ohms (Ω) • 3 things impact resistance • Length of wire (______ less resistant) • Width of wire (_______less resistant) • Temperature (_______ less resistant, less friction)

  12. OHM’S LAWRelationship between current, voltage and resistance • I=V/R or • Current in Ampere=Voltage/Resistance • 3part equation I R V

  13. Think of voltage as being how hard you turn the water on to your hose and current as how fast the water flows. • The harder you turn on your water the faster it flows (Voltage increases, current increases) • The water slows down if the hose is bent (current decreases, resistance increases)

  14. OHM’s LAW Example PROBLEMS • How much current does a headlight use with a 12-volt battery if it has a resistance of 3Ω? • V=12volts R=3ohms I=?amps • V=IR • 12/3=4 amps

  15. What is the of a 6 amp circuit with a resistance of 3Ω? • I=6amps, R=3ohms, V=? • V=IR • V=6x3 V=18V

  16. What is the resistance of a light bulb that uses 6 amps of electricity at 120volts? • V=120 I=6 Ω=? • V=IR • 120/6=20ohms

  17. Calculate the voltage difference in a circuit with a resistance of 25Ω if the current in the circuit is 0.5 A. • A current of 0.5A flows in a 60 watt lightbulb when the voltage difference between the ends of the filament is 120V. What is the resistance of the filament? • A circuit has a resistance of 4Ω. What voltage difference will cause a current of 1.4 A to flow in the circuit? • How may amperes of current will flow in a circuit if the voltage difference is 9V and the resistance is 3Ω? • If a voltage difference of 3V causes a1.5A current to flow in a circuit, what is the resistance?

  18. V=IR • 0.5x25=12.5V • 120/0.5=240Ω • 1.4x4=5.6V • 9/3=3A • 3/1.5=2Ω

  19. Electricity is useful because it is easily converted into another form of energy • Fan-electrical to mechanical • Light bulbs- electrical to heat and light • Hair Dryer- electrical to heat and mechanical

  20. Power-rate at which energy is converted from one form to another • P=IV • Power = Current x voltage • Measured in Watts (W)

  21. Power problem examples • A toaster oven is plugged into an outlet with 120V. How much power does the oven use if the current is 10A? • P=? I=10 V=120 • 10x120=1200W • A VCR that is not playing uses 10W of power. What is the current if it is plugged into a 120V outlet? • P=10 I=? V=120 • 10/120=0.83A

  22. A flashlight bulb uses 2.4W of power when the current in the bulb is 0.8A. What is the voltage difference? • P=2.4 V=? I=0.8 • 2.4/0.8=3.0V Electrical power is charged by the rate at which energy is used in kilowatts. Cost of appliance=energy used x cost of a kWh 100W light bulb is on for 5 hours at a cost of $0.10/kWH (100W=0.001kWh) E=0.001kWh x 5=0.5kWh x0.10=$0.05

  23. Electrical Circuits • Electrical Circuits have three parts: • Voltage difference- battery or generator at power plant ( • Resistor- device that uses electricity (hair dryer, light bulb, etc. • Conductor-wire which connects it all together, circuit must be closed for electrons to flow

  24. 2-types of circuits

  25. Series Circuit What is the current through the circuit to the right? When you add light bulbs to the Series circuit

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