1. Chapter 16

2.  Smallest particles of matter are called atoms  Electrons  Protons  Neutrons

3. Protons  Positive charge Electrons  Negative charge **If atom has equal number of protons & electrons there is no net charge***

4.  Charges produce a force between objects › Opposite charges attract › Like charges repel

5.  Electrons can be moved  Rubbing hair against a balloon will move some electrons from the hair to the balloon  Both the hair and the balloon will have a charge. › What will the charge on the balloon be? › What will the charge on the hair be?

7.  If there is an imbalance with the number of electrons and protons, there is a net electric charge  If there is more electrons than protons, object is negative › Electron’s charge = -1.6 x 10 -19 C  If there is more protons than electrons, the object is positive › Proton’s charge = 1.6 x 10 -19 C

8.  Conductor › allows electrons to move through it easily › e - are loosely held › ex: metals like copper and silver

9.  Insulator › material that doesn’t allow electrons to move through it easily › e - are tightly held › ex: plastic, wood, rubber, glass

10.  An electric field surrounds all charged objects.  Electric forces act at a distance because of this field.

11.  Static means not moving  Static electricity is electricity at rest  Friction can cause it  Objects rub together and electrons move from one object another.

12.  Eventually static electric charge will move.  Slowly the electrons may move into moisture in the air  Or quickly in a spark.

13.  Wind rubs particles in cloud together  Cloud gains charge  Induce charge in ground  Eventually a big charge jumps  Lightning rod protects buildings

14. Charging by friction  Electrons are transferred when different materials are rubbed together  Depends on materials Charging by contact (Conduction)  When negative object touches neutral object, electrons move objects Charging by Induction charging an object without actually touching the object to any other charged object

15.  Consists of: › Flask › Metal bar (conductor) through rubber stopper (insulator) › 2 pieces of thin foil on the bottom › Charge on the metal will push the foil apart because they have the same charge

16. No Charge- leaves hang straight down

17. Rod with negative charge

18. Rod with negative charge: Pushes negative charges away - down electroscope

19. Extra negative charges cause leaves to move apart

20. … Remove rod everything returns

21. Conduction Rod with negative charge

22. … Rod with negative charge touches electroscope

23. Electrons are transferred from rod to electroscope

24. Extra negative charges cause the leaves to move apart.

25. Remove rod leaves stay apart.

26.  Often called voltage  Change in the electrical potential energy of a charged particle divided by its charge  Occurs when charge moves from one place to another  SI Unit for potential difference is the Volt (V) › 1 V = 1 J/C

27.  Flow of electrons  Number of electrons move through a conductor  Measured in Amperes of Amps (A)

28.  Internal friction, which slows the movement of charges through a conducting material  A dim 40W bulb has a higher resistance than the filament of a bright 100W bulb  SI Unit is ohm (Ω) › Ω = Volts/Amps  Found by dividing the voltage across the conductor by the current

29.  electrical energy is converted to thermal energy & light  Resistance depends on… › the conductor (low) › Wire thickness  Less resistance in thicker wires › Wire length  Less resistance in shorter wires › Temperature  Less resistance at low temps Copper - low resistance Tungsten - high resistance

30.  The relationship among current, voltage, and resistance.  Ohm’s law states that the current in a circuit is equal to the voltage divided by the resistance  I = V R V I R

31. V = I × R V: potential difference (V) I: current (A) R: resistance (  ) Voltage ↑ when current increases. Voltage ↓ when resistance increases.

32.  A light bulb with a resistance of 160  is plugged into a 120-V outlet. What is the current flowing through the bulb? GIVEN: R = 160  V = 120 V I = ? WORK : I = V ÷ R I = (120 V) ÷ (160  ) I = 0.75 A I V R

33.  A car has a 12 volt system. The headlights are on a 10 amp circuit. How much resistance do they have?  Your house uses 120 volts. What amount of current would flow through a 20 ohm resistor?

34.  Circuit › Path through which electrons can flow

35. A - batteryC - light bulb B - switchD - resistor

36.  For current to flow there must be a complete loop  Electrons flow from negative to positive terminal  Work is done if there is a resistance in the wire.

37.  Series Circuit › current travels in a single path  1 break stops the flow of current › current is the same throughout circuit  lights are equal brightness › each device receives a fraction of the total voltage  get dimmer as lights are added

38. Series Circuits

40. Break in the wire turns off all the lights

41. Series Circuits

42.  Parallel Circuits › current travels in multiple paths  one break doesn’t stop flow › current varies in different branches  takes path of least resistance  “bigger” light would be dimmer › each device receives the total voltage  no change when lights are added

43. Parallel Circuit

45. P = I × V P: power (W) I: current (A) V: potential difference (V) rate at which electrical energy is converted to another form of energy

46.  A calculator has a 0.01-A current flowing through it. It operates with a potential difference of 9 V. How much power does it use? GIVEN: I = 0.01 A V = 9 V P = ? WORK : P = I · V P = (0.01 A) (9 V) P = 0.09 W I P V

47.  energy use of an appliance depends on power required and time used E = P × t E: energy (kWh) P: power (kW) t: time (h)

48.  The SI unit for energy is a joule.  Kilowatt-hour meters measure the electricity used in your home (kWh)

49.  A refrigerator is a major user of electrical power. If it uses 700 W and runs 10 hrs each day, how much energy (in kWh) is used in 1 day? GIVEN: P = 700 W = 0.7 kW t = 10 h E = ? WORK : E = P · t E = (0.7 kW) (10 h) E = 7 kWh P E t

50.  Direct current: electrons that flow in the same direction in a wire (DC) › From batteries  Alternating current: electrons that flow in different directions in a wire (AC) › From Genrators › Used in your home  Transformers change AC to DC

51.  Combination of parallel circuits › too many devices can cause wires to overheat  Safety Features: › fuse - metal melts, breaking circuit › circuit breaker - bimetallic strip bends when hot, breaking circuit

52.  Many appliances are equipped with a “ground” wire on the plug.  The ground wire prevents electric shock. The rounded third prong of a three-way electric plug is attached to the ground wire.  It constantly moves static electricity from the appliance to the ground.

53.  Broken wires or water can cause electric appliances to short-circuit.  A short circuit occurs when electricity takes a short path and bypasses the resistors in the circuit.  Because of this the resistance of the circuit is less and the circuit wire increases.  The increased current can produce enough heat to melt wires and start a fire, or cause serious electric shock.

54.  Fuses and circuit breakers protect against overloaded circuits.  A number on the fuse indicates the max. current that will flow through it.  Circuit breakers are often used in place of fuses. A circuit breaker is a switch that opens automatically when electric current in a circuit reaches its max.