Coulomb’s Law FeFe -F e r q1q1 q2q2 F e = k q 1 q 2 / r 2 k = 9 x 10 9 Nm 2 /C 2 rq1q1 q2q2 FeFe 111k rq1q1 q2q2 FeFe 211¼ k rq1q1 q2q2 FeFe 1212k 1224k rq1q1 q2q2 FeFe 111k 211¼ k 1212k 1224k 222k F e = k (1)(1)/ (1) 2 F e = k F e = k (1)(1)/ (2) 2 F e = ¼ k F e = k (2)(1)/ (1) 2 F e = 2k F e = k (2)(2)/ (1) 2 F e = 4k F e = k (2)(2)/ (2) 2 F e = k As r increases F e increases as the inverse square of r. As q increases F e increases in direct proportion to q.
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 electron charges 6,250,000,000,000,000,000 electrons 6.25 quintillion electrons Electron charge = 1.6 x coulombs Electron charge = 1/6.25 x coulombs Electron charge = coulombs
Induced Charges Simulation
Top 8 Conductors of Electricity 1.Silver 1.47 x Copper 1.72 x Gold 2.44 x Aluminum 2.63 x Tungsten 5.51 x Steel 20 x Lead 22 x Nichrome 100 x Aluminum Copper Gold Lead Nichrome Silver Steel Tungsten The following metals are listed in alphabetical order. Arrange them in order of conductivity from best to worst.
Ohm’s Law I = Current measured in amperes. V = Voltage measured in volts. R = Resistance measured in ohms. I = V/R 1 amp = 1 volt/1 ohm Current = Voltage/Resistance
Electric Power I = Current measured in amperes. V = Voltage measured in volts. P = Power measured in Watts. P = I x V 1 watt = 1 amp x 1 volt Power = Current x Voltage
Electric Power E = P t Energy = (Power)(time) You pay for electricity in kilowatthours (kwh) 1 kwh =(1000)(1J/s)(3,600s) =3,600,000 J Cost per kwh =$.10 (approximately)
Electric Power (cont) # kwh = (P x t)/1000 #kwh = 18 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? P = 600 watts t = 30 hours Cost = ? $ #kwh = 600 x 30/ kwh x $.10 /kwh = $1.80
Electric Shock What is the resistance of the human body? 500,000 Ώ If dry and insulated 100 ΏIf soaked in salt water.001 ampcan be felt.005 ampis painful.010 amp causes involuntary muscle contractions (spasms).015 ampcauses loss of muscle control).070 ampIf through the heart, serious disruption; probably fatal if current lasts for more than 1 second..10 ampAlmost always fatal. A B CD
Electric Shock (cont.) What are the effects of electric shock? 1. Muscle contractions and spasms. 2. Heating and burning. 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 ampDeath! 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? I = V/R= 120/100,000 =.0012 ampShock felt. I = V/R= 120/500,000 = ampNothing. 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?
Electric Circuit V - + R 1) Source of Voltage (Battery) 2) Device to convert energy (Resistor) 3) Complete conducting path (wires and switch)
Series Circuits V = V 1 + V 2 + V 3 I = I 1 = I 2 = I 3 Simulation Current is the same for all bulbs. The voltage across each bulb adds up to the total voltage of the battery. If one bulb goes out, they all go out.
Parallel Circuits VideoSimulation V = V 1 = V 2 = V 3 I = I 1 + I 2 + I 3 Voltage is the same for all bulbs. The current in each bulb adds up to the total current from the Battery. If one bulb goes out, the others stay on.