Parts of an atom. Protons (P + ) Electrons (e - ) Neutrons. Have a positive electric charge. Have a negative electric charge

Transcription

1 Electricity

2 Parts of an atom Protons (P + ) Have a positive electric charge Electrons (e - ) Have a negative electric charge Neutrons Are neutral Have no charge

3 Electric Charge In most atoms, the charges of the protons and electrons cancel each other out Atom has no net charge Atoms become charged by: GAINING AND LOSING ELECTRONS Can be detected by an electroscope

4 Static Electricity The accumulation of excess electric charges on an object

5 Static Electricity Activity Quickly and quietly find a partner and a pair of desks!

6 Static Electricity The accumulation of excess electric charges on an object

7 Law of Conservation of Charge Charge may be transferred from object to object, but it cannot be created or destroyed. Sound familiar? Law of Conservation of Energy

8 Opposites attract

9 Likes Repel

10 Charged atoms Electric field is generated by electrically charged particles and timevarying magnetic fields. Charges can act on each other even at a distance

11 More About Charge

12 Conductors and Insulators CONDUCTORS Materials that allow electrons to easily move through. Examples: Metals INSULATORS Materials that do not allow electrons to easily move through. Examples: Plastic Wood Rubber Glass

13 Let s explore HOW OBJECTS CAN BE CHARGED

14 Charging by Contact/Friction Process of transferring charge by touching or rubbing Example Rubbing your feet on the carpet and getting static electricity

15 Charging by induction Process of rearranging electrons on a neutral object by a nearby charged object Example A balloon that has been rubbed on your hair causing someone else s arm hair to move

16 Static discharge A transfer of charge through the air between two objects because of a buildup of static electricity Examples Lightning Spark from touching objects

17 Grounding Using a conductor to direct an electric charge to the ground Examples Lightning Rod

18 Copy the following into your notes: Electrical energy can be converted to: mechanical, thermal, and light energy. Electric Power is: The rate at which electrical energy is converted from one form to another (measured in Watts) Electric Power formula: P= I x V (Power=Current x Voltage difference) P=Power (W), I=Current (A), V=Potential difference (V) Electrical Energy formula: E=P x t (Energy=Power x Time) E= Energy (KwH), P=Power (W), t=time (h) Next, complete questions 8-14 on the Electricity Practice Calculations sheet given back to you today. If you missed any in 1-7, you should correct it. You have 25 minutes to do this; whatever is not completed today will be homework.

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20 Static Electricity the net accumulation of electric charges on an object Electric Field force exerted by an e - on anything that has an electric charge opposite charges attract like charges repel

21 Static Discharge the movement of electrons to relieve a separation in charge

22 Conductor material that allows electrons to move through it easily e - are loosely held ex: metals like copper and silver

23 Insulator material that doesn t allow electrons to move through it easily e - are tightly held ex: plastic, wood, rubber, glass

24 Electroscope instrument that detects the presence of electrical charges leaves separate when they gain either a + or - charge

25 The flow of charges (usually electrons) through a wire or conductor. Measured in amperes (A or amps)

26 ALWAYS flows from High to Low voltage A voltage difference is the push that causes charges to move. Measured in volts (V)

27 For charges to flow (to have current or voltage) a wire must always be connected in a closed path

28 A - battery B - switch C - light bulb D - resistor

29 Dry Cell Battery Produces a voltage difference between its zinc container and its carbon suspension rod Causes current to flow between them

30 Wet Cell Battery Contains two connected plates made of different metals (usually lead) in a connected solution (usually sulfuric acid) Car, truck and tractor batteries

31 Wall Socket Has a voltage difference across the two holes of an outlet. Generators at power plants provide the voltage difference

32 The tendency for a material to oppose the flow of electrons Changes electrical energy into thermal energy and light All materials have some electrical resistance Copper - low resistance Tungsten - high resistance

33 Measured in Ohms (Ω) Resistance increases with Increased length Decreased diameter Increased heat Think of a garden hose

34 Current = Voltage / Resistance V=Voltage I=Current R=Resistance

35 A lightbulb 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 =? V WORK: I = V R I = (120 V) (160 ) I = 0.75 A I R

36 What property of electric current causes light bulbs to give light?

37 Resistance. As electrons flow through the filament, the filament resists their flow and changes electrical energy into thermal energy and light.

38 Solve the Following: A light bulb is connected into a circuit and provides provides 5 ohms of resistance. How much voltage must be applied to insure a current of 15 amps will travel through the lightbulb? What is the voltage across a 12-ohm resistor with a current of 35 amps?

39 Rely on generators to produce a voltage difference across the outlet causing charge to move when the circuit is complete

40 Current only has one path (or loop) to follow Example: Some holiday lights

41 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 If any part of the circuit is broken, the current stops flowing

42 Current only has two or more paths (or branches) to follow Example: Electric system in a house

43 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

44 Use parallel circuits in a logical network Each branch receives the standard voltage from the electric company too many devices can cause wires to overheat

45 Enters your home at the circuit breaker/fuse box Branches out to all your outlets Like your Heart and blood vessels

46 Guards against overheating electric wires Contains a small piece of metal that melts if current becomes too high.

47 Guards against overheating electric wires Contains a small piece of metal that bends when it gets hot

48 Can be converted to Mechanical energy Thermal energy Light energy

49 The rate at which electrical energy is converted from one form to another Measured in Watts (W) Power = Current x Voltage Difference P (W) = I (A) x V (V)

50 P: power (W) P = I V I: current (A) V: potential difference (V)

51 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 =? P WORK: P = I V P = (0.01 A) (9 V) P = 0.09 W I V

52 Unit of electrical energy is the Kilowatt-Hour Equals 1000 Watts of power used for 1 hour Energy = Power x Time E (kwh) = P (kw) x t (h)

53 E = P t E: energy (kwh) P: power (kw) t: time (h)

54 A refrigerator is a major user of electrical power. If it uses 700 W and runs 10 hours each day, how much energy (in kwh) is used in one day? GIVEN: P = 700 W = 0.7 kw t = 10 h E =? E WORK: E = P t E = (0.7 kw) (10 h) E = 7 kwh P t

55 Does your home have a fuse box or circuit breaker? Why is it there? How does it work?

56 It is there to make sure the electrical wires in our home do not get too hot and start fires. If the wired get too hot, they melt the piece of metal in the fuse or bend the piece of metal in the circuit. This opens the circuit and stops the flow of current. If we have a fuse box, we have to replace the melted fuse with a new one. If we have a circuit breaker, we only need to unplug some appliances and flip a switch.

57 and its uses

58 force of attraction or repulsion between unlike or like poles due to the arrangement of electrons closely related to electricity

59 Interaction between two magnets Increases as distance decreases Bring your two magnets together-what happens?

60 The regions of a magnet where the magnetic force exerted by the magnet is strongest North and South

61 Magnetic Poles like poles repel unlike poles attract a broken magnet creates new poles!

62 Magnetic Field area around a magnet where magnetic forces act field lines show direction of field (N S)

63 Exerts magnetic force Surrounds a magnet Strongest closer to a magnet

64 A compass needle Is a small bar magnet that can freely rotate Always points NORTH

65 Magnetic Domain groups of atoms with aligned magnetic poles domain in a magnetized object, domains are all aligned

66 The magnetic field created by each atom exerts a force on nearby atoms Magnetic Materials Iron Cobalt Nickel Permanent Magnets Made by placing a magnetic material in a strong magnetic field forcing a large number of magnetic domains to line up

67 What formula would be used to solve the problem below? Use that formula to solve it: What materials allow charges to flow easily? What materials make it difficult for them to flow?

68 Produced by moving charges Field around a currentcarrying wire forms a circular pattern around the wire Strength depends on the amount of current flowing through the wire. Increased current = increased magnetic field

69 Electromagnet strong, temporary magnet formed when current is passed through a coil of wire surrounding an iron core acts like a bar magnet when current is on

70 Battery- Magnetic field is only present when current is flowing through the wire coil Field strength Can be increased by increasing the number of coils Can be increased by increasing the current flowing through wire

71 A device that uses an electromagnet to measure electric current Gas gauge-sensor attached to float

72 Speaker electrical energy mechanical energy wire coil moves back & forth as its magnetic field interacts with the field of a fixed magnet forced vibration causes the cone to move sound

73 Motor electrical energy mechanical energy electromagnet rotates between the poles of a fixed magnet commutator reverses the poles of the magnet

74 assembled motor armature & commutator brushes & wires to battery field magnet

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76 Contains an electromagnet that is free to rotate between the poles of a permanent, fixed magnet. Coil in the electromagnet is connected to the source of current.

77 Changing the direction of the current causes the coil in the motor to keep rotating Rotation speed of motors can be controlled Vary amount of current More current = stronger magnetic field = magnetic force b/w coil and permanent magnetic increases = coil turns faster ug4ry

78 Complete the front side of your study guide. We will review this together. Remember, the study guide will be checked and needs to be completed!

79 Electromagnetic Induction producing a current by moving a wire through a magnetic field some microphones work just like minispeakers in reverse sound waves cause coil to move current Coil Dynamic Microphone

80 Electricity used in a home comes from a power plant with huge generators. Coils of electromagnets usually connected to a turbine (a large wheel that rotates when pushed by water, wind or steam.)

81 Electric Generator mechanical energy electrical energy armature is rotated between magnet poles magnetic field induces a current in the wire coil MOTOR GENERATOR

82 Hydroelectric Dam PE of lake water is converted to KE mechanical KE turns the generator shaft which creates electrical energy

83 Direct Current (DC) current flows in one direction dry cells Alternating Current (AC) current reverses its direction at regular intervals electrical outlets

84 Current that flows in only one direction through a wire

85 Reverses the direction of the current flow in a regular way In North America: 60 cycles per second = 60 Hz Changes directions 120 times each second

86 Transformer increases or decreases AC voltage primary coil AC produces a magnetic field that induces AC in the secondary coil voltage ratio = ratio of turns in each coil

87 Step-up Transformer increases the voltage more turns power plants Step-down Transformer decreases the voltage fewer turns household appliances (hairdryers, etc.)

88 J8EY