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Electricity

Electricity. Charging by Rubbing. +. -. Charged Objects. Add + Charge. +. Remove - Charge. -. Add - Charge. Remove + Charge. Simulation. -. +. +. +. Electric Force. Simulation. -F e. F e. q 1. q 2. r. F e = k q 1 q 2 / r 2. Coulomb’s Law. k = 9 x 10 9 Nm 2 /C 2.

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Electricity

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  1. Electricity

  2. Charging by Rubbing + -

  3. Charged Objects Add + Charge + Remove - Charge - Add - Charge Remove + Charge Simulation

  4. - + + + Electric Force Simulation

  5. -Fe Fe q1 q2 r Fe = k q1 q2/r2 Coulomb’s Law k = 9 x 109 Nm2/C2 Fe = k (1)(1)/(1)2 Fe = k Fe = k (1)(1)/(2)2 Fe = ¼ k Fe = k (2)(1)/(1)2 Fe = 2k Fe = k (2)(2)/(1)2 Fe = 4k Fe = k (2)(2)/(2)2 Fe = k As r increases Fe increases as the inverse square of r. As q increases Fe increases in direct proportion to q.

  6. The Unit of Charge 1 Coulomb is a very large amount of charge. The unit comes from the definition of electric current. 1 ampere = 1 coulomb/second 1 coulomb = 6.25 x 1018 electron charges 6,250,000,000,000,000,000 electrons 6.25 quintillion electrons Electron charge = 1/6.25 x 1018 coulombs Electron charge = 1.6 x 10-19 coulombs Electron charge = .00000000000000000016 coulombs

  7. - + - + - + + + + + + + + + + + + + + + + + + + + - + - + - + + + + + + + + + + + + + + + + + + + + + + + + + + + + Induced Charges - + - + - + Simulation

  8. 50- 50- 100- 0 Grounding 75- 25- 99- 1- 0 100- Earth

  9. The following metals are listed in alphabetical order. Arrange them in order of conductivity from best to worst. Top 8 Conductors of Electricity Aluminum Copper Gold Lead Nichrome Silver Steel Tungsten • Silver 1.47 x 10-8 • Copper 1.72 x 10-8 • Gold 2.44 x 10-8 • Aluminum 2.63 x 10-8 • Tungsten 5.51 x 10-8 • Steel 20 x 10-8 • Lead 22 x 10-8 • Nichrome 100 x 10-8

  10. Ohm’s Law Current = Voltage/Resistance I = V/R 1 amp = 1 volt/1 ohm I = Current measured in amperes. V = Voltage measured in volts. R = Resistance measured in ohms.

  11. Power = Current x Voltage Electric Power P = I x V 1 watt = 1 amp x 1 volt I = Current measured in amperes. V = Voltage measured in volts. P = Power measured in Watts.

  12. Electric Power Energy = (Power)(time) E = P t You pay for electricity in kilowatthours (kwh) 1 kwh = (1000)(1J/s)(3,600s) = 3,600,000 J Cost per kwh = $.10 (approximately)

  13. A 600 watt hair dryer is operated for 1 hour per day for 30 days. If the electric company charges $.10 per kilo-watt-hour, what is the cost to operate the dryer? Electric Power (cont) # kwh = (P x t)/1000 #kwh = 600 x 30/1000 #kwh = 18 18 kwh x $.10 /kwh = $1.80 P = 600 watts t = 30 hours Cost = ? $

  14. A C D B Electric Shock What is the resistance of the human body? 500,000 Ώ If dry and insulated If soaked in salt water 100 Ώ .001 amp can be felt .005 amp is painful causes involuntary muscle contractions (spasms) .010 amp .015 amp causes loss of muscle control) .070 amp If through the heart, serious disruption; probably fatal if current lasts for more than 1 second. .10 amp Almost always fatal.

  15. What are the effects of electric shock? Electric Shock (cont.) 1. Muscle contractions and spasms. 2. Heating and burning. A dry person standing on a wood floor has a resistance of 500,000 Ώ. He comes in contact with a 120 volt “hot” electric wire. What happens? = .00012 amp Nothing. I = V/R = 120/500,000 A dry person standing on a concrete floor has a resistance of 100,000 Ώ. He comes in contact with a 120 volt “hot” electric wire. What happens? = .0012 amp Shock felt. I = V/R = 120/100,000 A wet swimmer standing on a concrete floor has a resistance of 500 Ώ. He comes in contact with a 120 volt “hot” electric wire. What happens? I = V/R = 120/500 = .24 amp Death!

  16. R + V - Electric Circuit 1) Source of Voltage (Battery) 2) Device to convert energy (Resistor) 3) Complete conducting path (wires and switch)

  17. Series Circuits Current is the same for all bulbs. I = I1 = I2 = I3 The voltage across each bulb adds up to the total voltage of the battery. V = V1 + V2 + V3 If one bulb goes out, they all go out. Simulation

  18. Parallel Circuits Voltage is the same for all bulbs. V = V1 = V2 = V3 The current in each bulb adds up to the total current from the Battery. I = I1 + I2 + I3 If one bulb goes out, the others stay on. Simulation Video

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