Electricity CHARGE. q = 1.6 x10-19 C

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2 Electricity CHARGE q = 1.6 x10-19 C

3 How many protons in a Coulomb? C x (1 proton) / (1.60 x 10 C) = x10 protons!

4 Opposites Attract

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7 Most materials are Electrically NEUTRAL (lowest potential energy)

8 TOTAL charge is conserved for any process. Net Zero Charge Net Zero Charge

9 TOTAL charge is conserved for any process. Net Charge is still zero after rubbing

10 Electric forces for charges that are not moving. Though static charge DO move! But not continuously as with current. Static Cling: Adhesion

11 Coulomb s Law F = Force between q and q : qq k = 9 x 10 9 N m 2 /C kq q r Likes Repel: Opposites Attract:

12 What is the Electric Force between two electrons separated by 1 μm? k = 9 x 10 9 N m 2 /C 2 q e = -1.6 x10-19 (C) F = = = kq1q2 2 r (9.00x10 Nm / C ) x(1.60x10 C) 6 2 (10 m) 2.30x N

13 What is the acceleration of one of the electrons? k = 9 x 10 9 N m 2 /C 2 q e = -1.6 x10-19 C 31 me = 9.019x10 kg a = = = F / m x10 N / 9.019x10 kg x10 m/ s

14 How strong is the Coulomb Force relative to Gravity? proton electron F C = kq q r F k = 9 x 10 9 N m 2 /C 2 G = Gm m r G = 6.67 x10-11 N m 2 /kg 2 q e = 1.6 x10-19 C m p = 1.67 x10-27 kg, m e = 9.11 x10-31 kg r = 5.30 x10-11 m

15 How strong is the Coulomb Force relative to Gravity? proton electron F C = kq q r F G 47 8 = F = 8.20x10 N C F = 3.61x10 N G Gm m r F / F = 2.27x10 C G 39

16 Electric Field Shows how the field acts on a POSTIVE charge! E = Force/unit Charge

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22 What Direction are the Electric Field Lines?

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27 The Electric Field does work on the charge to move it from A to B, converting HIGH V Potential Energy into Kinetic Energy, same as with the gravitational field. The Electric Potential Energy per unit charge between A and B is called the Electric Potential Difference between A and B. - Δ V = V V B A - LOW V

28 Electric Potential Δ V = V V Unit for Electric Potential is the VOLT: 1 V = J/C = N m /C Electric Potential is a SCALAR! B Only DIFFERENCES in potential between two points can be measured. There is no potential for a single point! Electric Potential is NOT Potential Energy! + charges move from hi to low potential (think gravity water fall) - charges move from low to hi potential (think antigravity water pump) A

29 Equal Distance Equal Force A B C

30 Equal Potential A B C

31 Equipotential Lines A B C

32 Where is the Potential Highest? A, B, C? A B C

33 The Electric Field is the Slope of the Electric Potential!

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36 Sources of Electric Potential: Batteries 1.5 Volt Battery is the Voltage across the terminals.

37 Example A 12V motorcycle battery moves 5000C of charge. How much energy does it deliver to that charge? Δ PE =ΔVq 0 = 12 V(5000 C) = 12 J / C(5000 C) V = 12V = x10 J Potential (Voltage) is NOT Energy!

38 Positive Charges move from HI to LOW potential. HI V LOW V

39 Negative Charges move from LOW to HI potential. HI V LOW V

40 HOW FAST DO ELECTRONS MOVE IN A CURRENT CARRYING CONDUCTING WIRE??

41 Electron Speed is called the DRIFT Velocity. Drift velocity ~.001 m/s!!! Electric Fields travel at the speed of light!

42 Current I = Coulomb/second = Ampere Current flows from a higher potential to a lower potential (electrons flow the opposite way). Current carrying wires are neutral! DC current flows in one direction AC current oscillates back and forth Electrons have a drift velocity of.001m/s! Electric Fields travel at speed of light

43 Conductivity Conductors: loosely bound electrons; charge flows freely Ex: metals, salt water Insulators: tightly bound electrons; charge hard to move Ex: organic materials, wood, glass, water Electrons move, protons are bound in a lattice Positively charged ions flow in fluid (liquid or gas) Positive & Negative charges rearrange and become Polarized in Insulators

44 Resistance

45 Resistance: Resistivity The LONGER the wire the GREATER the R The THINNER the wire the GREATER the R The HOTTER the wire the GREATER the R

46 When are light bulbs more likely to blow? When hot or cold? The HOTTER the wire the GREATER the R! At lower Resistance, the bulb draws more current and it blows the filament!

47 Electrical Power As a charge moves from a to b, the electric potential energy of the system increases by QΔV The chemical energy in the battery must decrease by this same amount As the charge moves through the resistor (c to d), the system loses this electric potential energy during collisions of the electrons with the atoms of the resistor This energy is transformed into internal energy in the resistor as increased vibrational motion of the atoms in the resistor P = IV

48 POWER: P = IV Energy time J s [ P] = = = Watt P = IV You pay for ENERGY not for ELECTRONS! Kilowatt-hour is the energy consumed in one hour: [kwh]=j NOT TIME! Power x Time

49 QUESTION The voltage and power on a light bulb read 120 V, 60 W How much current will flow through the bulb? USE: P = IV I = P/V = 60 W/120 V = 1/2 Amp

50 Ohms Law: V = IR

51 QUESTION The power and voltage on a light bulb read 120 V, 60 W What is the resistance of the filament? (I =.5 A) Hint: USE OHMS LAW: V = IR R = V/I = 120 V/.5 A = 240 Ω

52 If V = 120V, What is I? USE P = IV=> I = P/V Appliance _ Power Current (A) Hair Dryer Electric Iron TV Computer 1600 Watts 1200 Watts 100 Watts 45 Watts

53 If V = 120V, What is I? USE P = IV=> I = P/V Appliance _ Power Current (A) Hair Dryer 1600 Watts 13.3 A Electric Iron 1200 Watts 10 A TV 100 Watts.83 A Computer 45 Watts.38 A

54 Electric Bill: Cost to run for 1 $.05 per 1 kw-hr? Cost = Power x Time x Rate Appliance _ Power Cost Hair Dryer Electric Iron TV Computer 1600 Watts 1200 Watts 100 Watts 45 Watts

55 Electric Bill: Cost to run for 1 $.05 per 1 kw-hr? Cost = Power x Time x Rate Appliance _ Power Cost Hair Dryer 1600 Watts $0.08 Electric Iron 1200 Watts $0.06 TV 100 Watts $0.005 Computer 45 Watts $0.003

56 Series Circuits The current is the same in each device. The equivalent resistance of the circuit is the sum of the individual resistances. Parallel Circuits The voltage of each device is the full voltage of the EMF source (the battery) The total current is divided between each path: = + R R R total 1 2 R = R + R total 1 2

57 Circuits Problem:Bulbs in Series vs Parallel A circuit contains a 48-V battery and two 240Ω light bulbs. In which circuit does each bulb burn brighter? RULE: THE MORE POWER DISSIPATED IN A BULB, THE BRIGHTER IT IS. P= IV Parallel Bulbs Burn Brighter!

58 Circuits Problem:Bulbs in Series vs Parallel If a bulb burns out - what happens to the other bulb in each circuit? Does it go out? Is it brighter? Dimmer? Or? In the series circuit, the burned out bulb will short the circuit and the other bulb will go out. In the parallel circuit the other bulb will have the same brightness.

59 Circuits Problem:3 Bulbs in Parallel If one more bulb is added to each circuit (3 bulbs total), how does the brightness of the bulbs change? Or not? In the parallel circuit, the bulbs DO NOT DIM. WHY? In parallel, each of the three equal bulbs gets the full voltage of the battery source. Is this getting something for nothing? NO! Parallel circuits drain the battery faster!

60 Parallel Circuits As the number of branches is increased, the overall resistance of the circuit is DECREASED. Overall resistance is lowered with each added path between any two points of the circuit. This means the overall resistance of the circuit is less than the resistance of any one of the branches!!!! (Weird?) As overall resistance is lowered, more current is drawn. This is how you blow fuses!

61 QUESTION The power rating for two light bulbs read 30W and 60W. Which bulb has the greatest resistance at 120V? 2 2 P = V / R R= V / P R V W 2 = (120 ) / 30 = 480Ω R V W 2 = (120 ) / 60 = 240Ω (fyi: Power ratings are for bulbs in parallel only!)

62 Fuses If the current drawn exceeds safe levels, the fuse melts and the circuit breaks most house have switches, not fuses.

63 Current: Dead or Alive DEATH: NEUROLOGIC CRITERIA: An individual with irreversible cessation of all brain function, including the brain stem, is dead. CARDIOPULMONARY CRITERIA: An individual with irreversible cessation of circulatory and respiratory function is dead.

64 GE & Edison: We bring good things to light. More than a 1000 killed since 1890! The first electric chair, which was used to execute William Kemmler in 1890 Nebraska: Only state that requires it. 15-second-long jolt of 2,450 volts of electricity (~ 8 Amps)

65 Electric Shock Therapy ELECTRO CONVULSIVE THERAPY An electric shock is applied to produce a convulsive seizure. The shock is typically between volts and lasts between 0.5 and 1 seconds. No explanation of how it works. Used in the treatment of: 1.Chronic endogenous depression 2.Bipolar disorder. 3.Acute mania. 4.Certain types of schizophrenia In the U.S. 33,000-50,000 people receive ECT each year

66 Electric Shock What causes electric Shock in the human body, Voltage or Current? Electric Shock occurs when current is produced in the body, which is caused by an impressed voltage. Voltage is the CAUSE Current does the DAMAGE

67 Electric Shock Current (A) Effect Can be felt Painful Causes involuntary muscle spasms Causes loss of muscle control If through heart, serious! If current lasts for 1 s - FATAL! Dry Skin Body Resistance: 500,000 Ω Wet Skin Body Resistance: 1000 Ω

68 Frequency Matters

69 Question What current would you draw if you were unfortunate to shortcircuit a 120 V line with dry hands? Wet hands? Use Ohm s Law! V = IR! Dry Skin Body Resistance: 500,000 Ω Wet Skin Body Resistance: 1000 Ω

70 Question What current would you draw if you were unfortunate to shortcircuit a 120 V line with dry hands? Wet hands? Use Ohm s Law! V = IR! DRY: I = V/R = 120 V/500,000 Ω = (live!) WET: I = V/R = 120 V/1000 Ω =.12 (dead!)

71 Electrical Safety

72 Electrical Safety: Grounding

73 Electrical Safety: Grounding