1 Electricity

2 Electrons + + Negative Charge ELECTRICITY comes from the electrons in an atom.

3 Electricity Forms when electrons are transferred between objects.

4  Flow of electricity through wires Static Electricity Current Electricity  Build-up of electrical charge Types of Electricity  Electrons move in non-specific directions  Electrons move in definite paths

5 Static Electricity Lightning Zap! Electricity exists naturally in nature… For example:

6 Electric Charge The source of static in lightning and shocks are electric charges Most objects tend to be

7 Electric Charge coulomb (C) –the unit of electric charge –carried by 6.24 billion, billion electrons

8 Neutral ObjectCharged Object Net Charge: Net Charge of Objects:

9 Opposite Charges Attract + - Same Charges Repel Law of Electrical Charges

10 How do balloons stick to walls? Negative charges in the wall repel from the balloon. 1. Rub a balloon on a sweater to “charge it up.” The balloon sticks because the positive charges left over are attracted to the balloon.

11 The Electroscope 2 Gold “leaves” Metal rod Electricity can move down the metal rod to the two gold leaves.

12 The Electroscope When a rubber comb with a build-up of static electricity is touched to the rod builds up on both sides of the gold strip. Since the charge of the leaves are both negative the two sides of the strip repel one another.-- …the electric charge travels down the rod AND...

13 A battery uses chemical energy to move electrical charges.

14 + Circuits flow in a circular path

15 Energy in a Circuit... is similar to water through pipes We will learn how to measure the energy in a circuit and how... are related. and

16+ Light will not go on not connected no current will flow. because the wire is not connected to the battery; no current will flow.

17+ Light bulb turns on because the electrical current can now flow through the complete circuit.

18 Short Circuits an accidental path for current to flow often causing risk of shock or fire a branch with zero or very low resistance

19 Circuit Diagrams Wire Power Source (1.5 V) Bulb Resistance Switch+ openclosed

20 Energy Conversions in a Simple Circuit ChemicalEnergy Electrical Energy Light Energy and Thermal Energy If you add a light bulb in the circuit, electrical energy is converted into... Battery converts Chemical Energy into...

21 Measurement of energy IF = 1.5 volts 1.5V 3.0V ?V

V 0.0 V The potential difference (voltage) is 1.5 V. Potential Energy (height) To Lower Energy Potential Difference Voltage is a measure of “potential difference.” 1.5 Meters The unit for voltage is volts (V)

23 Voltage Higher Potential energy (height) To Lower Energy Potential Difference Greater Potential Difference 3.0 V 0.0 V The potential difference (voltage) is 3.0 V. The higher the energy, the greater the voltage (potential difference). 3.0 Meters

24 Current rate is the rate of the flow of an electrical charge. + How fast is this water coming out? How fast (speed) is the electricity flowing through these wires? rateCURRENT The rate that the electricity flows is called CURRENT CURRENT (I) is measured in Amperes (Amps).

25 TYPES of CURRENT Direct Current (DC) flows in one direction. Alternating Current (AC) flows back and forth.

26 Which of the pipes below would allow water out faster? The smaller pipe would have more resistance to the flow.RESISTANCE

27 Resistance (R) is measured in ohms. 

28 to Electrical Current Which of the following do you think would be most resistant to electrical current? Plastic Rubber Glass

29 These materials allow electrical charge (current) to move easily through them. They have little resistance to the flow of electrical current. They are

30 These materials do not allow electrical charges (current) to move easily through them. They have a strong resistance to the flow of electrical current. Plastic Rubber Glass They are

31 Conductors and Insulators: Insulators do not allow charges to flow easily –Examples include glass, plastic, and rubber Copper Wire Conductors allow charges to flow easily. –Examples include copper, silver, and aluminum. Rubber insulation

32 Semiconductors material that falls between conductor and insulator in terms of electrical conductivity computer chip, LED’s, some lasers electrical conductivity property of a material to allow charge to flow will carry a current

33 Wires carry an electrical charge. The “human” wiring system: The neuron (nerve cell) Insulation (Myelin Sheath, fatty tissue) Wires (nerve fibers) Copper wire covered in rubber insulation

34 Wire sizes Wires come in different sizes Thicker wire less resistance Gauges-measurement of thickness –18 gauge, 16 gauge, 14 gauge, 12 gauge Bigger the gauge #, thinner the wire, more resistance Lower gauge # (fatter) wire, less resistance

35 Resistance Current Voltage How Fast? How much? How much is it slowed down? Match the word on the left to the phrase on the right. (R) in Ohms  (I) in Amps (V) in Volts

36 Household Current Alternating current direction of the current goes back and forth, 60 times per second, example wall socket, 120 volts Direct current current flows in one direction batteries only-AAA, AA, C, D cell batteries all are 1.5 volts each, the difference in size means it should last longer

37 Safety devices fuse-small piece of metal that melts if the current becomes too high opening switch circuit breaker-piece of metal that bends when it gets over heated opening switch because current is too high GFI-ground fault interrupter, usually found in bathrooms or garages shuts off plug when current if too high.

38 Electrical Measuring Instruments Voltmeter-used in parallel to measure voltage Ammeter-used in series to measure current Galvanometer-use to detect a current Ohmmeter-measures resistance

39 We can use this formula to figure out volts, current and resistance. Georg Simon Ohm

40 Ohm’s Law Information If voltage goes up, the charges move a little faster between atoms and we get more current. Resistance of metals increases with temperature, because the particles collide more often causing more resistance. A current vs. voltage graph shows us if resistance changes.

41 Resistors Components that are used to control current in many circuits Fix resistors always has the same value Example 3-way light switch-each level connects to a different resistor, the 3 levels of current control the brightness of the bulb Variable Resistors as you turn the switch it changes the resistance, which in turn changes the current increase current, resistance is lower, brighter bulb Example-dimmer switch

42 Calculating Ohms Law Divide Multiply V volts I amps R ohms And, to find Resistance, we need to DIVIDE voltage by current. R = V I So, to find Current, we need to DIVIDE voltage by resistance. I = V R

43 Calculate the potential difference (volts) across a 3  resistor if a 0.5 A current is flowing through it. V = I x R What do you know? V = I = R = 0.5 A 3  ? V = 3  0.5 Ax V = 1.5 Volts

44 A radio with a resistance of 240  is plugged into a 120 V outlet. What is the current flowing from the outlet? V = I x R What do you know? V = I = R = 120 V 240  ? 120 V = 240  Ix 0.5 amps = I

45 Electrical Power is rate at which energy flows Power = current x voltage Power is measured in Watts P = I x V Divide Multiply P I V watts ampsvolts So, to find Current, we need to DIVIDE power by voltage. I = P V And, to find Voltage, we need to DIVIDE power by current. V = P I

46 Electrical Power Problem If a CD player uses 4.5 V with 0.2 amps of current, what is the power it uses? P = I = V = 0.2 A 4.5 V ? P = 0.2 A x 4.5 V P = 0.9 Watts P=I x V

47 Electrical Energy Electrical Energy = power x time Is measured in kilowatt-hours Kilo means 1000x E = P x t Divide Multiply E kWhr P kW t hr So, to find power, we need to DIVIDE energy by time. P = E t And, to find time, we need to DIVIDE energy by power. t = E P

48 Electrical Energy Problem You use your hairdryer for 10 minutes everyday. The hairdryer uses 1000 kilowatts. How many kilowatt-hours does your hairdryer use in 6 days? E = P = t = 1000 kW 6 days x 10min = 60 min or 1 hr E = 1000 kW x 1 hr 1000 kWhr E = P x t

49 Types of Circuits What is the difference between the wiring?

50 Series Circuits + The light bulbs turn on. However, since the voltage drops, the lights are dimmer..75 V Battery is 1.5 V

51 Series Circuits+ If this light bulb does not turn on, neither light bulb will turn on. This is because the circuit is broken here; so the current can’t flow to this bulb here. Burned out light bulb Battery is 1.5 V Christmas lights are commonly made this way.

52 Series Circuits Info The current has only one path it can travel along One light goes out all lights out-open circuit Imagine if you turned off one light in your house that means that the circuit is broke and everything else goes off. Everything would have to be turned on to keep things running. Current is the same at all points Voltage is reduced by each resistance (light bulb, motor, heaters) Voltage drop-each separate resistor causes volts to drop

53 Kirchhoff’s Voltage Law The total of all voltage drops must add up to the total voltage supplied by the battery (energy in) +1.5 V - 0.5V V V = 0 battery bulb bulb bulb

54 Parallel Circuits Current divides and has more than one path. +

55 Parallel Circuits + The current divides because it has more than one path to flow. Even though the path is stopped, the other light turns on because its circuit is not broken. Burned out light bulb Your house is wired with parallel circuits. Why do you think this is so?

56 Parallel Circuit Info contains separate branches for current to move through potential difference (volts) same at each branch one light off, use other branches to transfer current voltage is the same across all branch points (think of them as separate series circuits connected to a battery) each branch does NOT always have the same current, depends on how much resistance is in each branch, (desk lamp, power saw)

57 Kirchoff’s Current Law If current flows into a branching point, the same total current must flow out again.