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2 SCIENCE 9 UNIT 3 ELECTRICITY

3 Remember: In the last unit we learned that all matter is made up of atoms atoms have subatomic particles called, protons, neutrons and electrons neutrons and protons are inside the nucleus and the electrons move around outside neutrons have no charge, protons are positive and electrons are negative when the number of protons is equal to the number of electrons the object is neutral

4 Friction and Electron Transfer Friction occurs when objects rub against each other This can cause electrons to transfer from one object to the other

5 Friction and Electron Transfer Friction occurs when objects rub against each other This can cause electrons to transfer from one object to the other If electrons are removed from a neutral object it becomes positively charged If electrons are added to a neutral object it becomes negatively charged

6 Static charge is when an electric charge can be collected and stored in one place (can be + or -) Static discharge is the removal of a charge on an object

7 Measuring charge the unit of electric charge is the coulomb (C ) the addition or removal of electrons (or 6.25 x ) is 1 C A lightning bolt is C A flash on a camera is about C

8 Conductors and Insulators Some objects allow electrons to transfer more easily than other objects Insulators- materials that do not allow charges to move easily glass, plastic, and dry wood are good insulators Conductors- materials that allow electrons to move very easily metals are usually good conductors

9 Laws of Static Charge Opposite charges attract Like charges repel

10 Laws of Static Charge Opposite charges attract Like charges repel Neutral objects are attracted to charged objects

11 Laws of Static Charge Neutral objects are attracted to charged objects ex. Charged balloon sticking to a wall - when the negatively charged balloon moves close to the wall, electrons are repelled and move away, this means the side of the all closest to the balloon is more positive, attracting the balloon.

12 Uses of Static Electricity Photocopiers Electrostatic air cleaners Painting automobiles Plastic sandwich wrap

13 Dangers of Static Electricity Vehicles Airplanes and cars build up static charge This could result in a spark during fueling that could cause a fire Lightning is caused by static electricity &feature=iv&src_vid=fzNk4w2k2h0&v=L1HhRAUqFqM

14 Chapter 8 Electrical potential, current and resistance

15 Energy : the ability to do work Two major types of energy: Kinetic (energy due to motion) and potential (stored energy) Examples of potential energy

16 Electrical potential energy: stored electrical energy example- in a cell or battery

17 Electrical potential difference: The difference in potential energy from one point to another

18 Electrical potential difference: The difference in potential energy from one point to another Also called voltage Measured in volts (V) Measured using a voltmeter

19 Electrochemical cell: A device that converts chemical energy into electric energy 2 or more cells connected together are called a battery Electrochemical cells are made of: 2 electrodes (usually 2 different metals) An electrolyte (solution that conducts electricity) electrodes electrolyte

20 How electrochemical cells work (p.253): 1. electrolyte attacks metal A - pulling off atoms 2. as atoms are removed, the electrons are left behind 3. metal A has a negative charge Metal A

21 How electrochemical cells work (p.253): 4. electrolyte pulls electrons off of the metal B- 5. Metal B has a positive charge Metal B

22 How electrochemical cells work (p.253) 6. because there is an opposite charge on each electrode there is a potential difference (voltage) between the electrodes Metal B Metal A

23 The amount of voltage produced by the cell depends on what electrodes and electrolyte are used Most cells produce V Multiple cells are put together to make batteries with higher voltage (ex. 12 V car battery)

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25 Recall: Static electricity: electric charge that builds up on the surface of an object can be discharged but does not continue to flow In contrast to static electricity, current electricity is flowing

26 Current electricity: The continuous flow of charge in a complete circuit Current: The amount of charge passing a given point per second Symbol for current is I Measured in amperes (A) Measured using an ammeter

27 Think of charge like water, current electricity would be a river. The voltage (potential difference) would be the slope of the river. Current would be how much water passes a point in a given amount of time. Low Current High Current

28 Electrical resistance: Factor that slows down the flow of electrons symbol for resistance is R Measured in ohms (Ω) Resistance is the ratio of voltage to current

29 The relationship between resistance, voltage and current is called Ohm s Law We use the triangle below to represent the 3 forms of the equation V R= V I= V V= I x R I R I R

30 Converting Prefixes milli (m) is 1 thousandth (ex. 25mA= = A) kilo (k) is 1 thousand (ex. 5 kω = 5 x 1000= 5000Ω) mega (M) is 1 million (e. 12 MV =12 x = V) * note that milli is a lowercase m, mega is an uppercase M When solving problems, always convert units before calculating

31 Example: What is the voltage of a 12kΩ load that allows a current of 6mA? R= 12 kω = 12x 1000 Ω = Ω I = 6mA = A = A V = I x R x = 72 V

32 Resistance cont As the resistances slows the flow of electrons it converts electrical energy into other types of energy such as heat and/ or light In a light bulb, current is passed through a filament which has a very high resistance and a lot of the energy is transformed into light

33 Factors affecting the resistance of a conductor: Factor Material Thickness/ Diameter Predicted Affect Actual Affect Certain materials have greater resistance than others (ex. Iron much greater than copper) Increasing diameter/ thickness reduces resistance Length Temperature Increasing length increases resistance Increased temperature increases resistance

34 Think about it What happens to the current in a circuit if the thickness of the wire is increased while voltage stays constant?

35 Resistor:An electrical component which has a specific resistance These can be placed in a circuit to control current or voltage They are marked with coloured bands to identify their resistance value

36 Electric Circuit: A complete pathway that allows electrons to flow 4 Basic components of a circuit: 1.Source 2.Load 3.Conductor 4.Switch

37 Electric Circuit Symbols: *You may see some alternate symbols but we will try to use the ones listed here as they are consistent with your text book

38 Electric Circuit Diagrams Use a ruler, all wires should be straight, all corners 90 0 (right angles) Do not cross conductors/ wires if possible Final drawing should be a square or rectangle

39 Chapter 9 Series & Parallel Circuits, Energy, Power & Efficiency

40 Recall: Electric Circuit: A complete pathway that allows electrons to flow There are different types of circuits Simple -1 source 1 load Series - More than 1 load - 1 path Parallel - More than 1 load - Multiple paths

41 Prepare the foldable provided and use it to complete the worksheet

42 Ex. Christmas lights Voltage is divided between loads Ex. 12V source with 2 bulbs = 6V at each bulb Current is the same throughout the circuit (3A total = 3A each bulb) Adding a resistor in series increases resistance of the circuit Any point in the circuit breaks, entire circuit stops

43 Ex. Home ceiling lights Voltage is the same at each load (bulb) Ex. 12V source with 2 bulbs = 12V at each bulb Current is divided between loads ex. 3A total = 1.5A at each bulb Adding a resistor in parallel decreases resistance of the circuit Some points in the circuit can break while others continue

44 Series and Parallel

45 Series and Parallel P Questions 2-6

46 Pro Con Series Connecting cells in series will give a higher voltage Current is constant through the circuit If one part of the circuit breaks, the whole circuit stops Parallel Current can still flow if there is a fault in part of the circuit Each load gets equal voltage Cells in parallel have longer life Requires more wires Use Cells in a flashlight (brighter) Cells in a lighthouse

47 Protecting Household Circuits (p.296) The circuits in homes are protected by circuit breakers Incoming power is fed to a service panel then moves out to different circuits in the home

48 Protecting Household Circuits (p.296) When current is too high, a metal strip in the breaker heats up, bends, and opens the circuit This is called tripping the breaker Current stops until the breaker is reset

49 Protecting Household Circuits (p.296) When current is too high, a metal strip in the breaker heats up, bends, and opens the circuit This is called tripping the breaker Current stops until the breaker is reset Older homes used fuses which would need to be replaced

50 Protecting Household Circuits (p.296) Many loads also include a ground provides a path for excess current to flow if it is leaked into metal components of the circuit Ground

51 Electrical Energy (E): The ability to do work Measured in Joules (J) Electrical Power (P): The rate work is done or energy is transformed Measured in Watts (W)

52 Electrical Energy (E): The ability to do work Measured in Joules (J) Electrical Power (P): The rate work is done or energy is transformed Measured in Watts (W) E E energy (J) P Power (W) t Time (sec) P t

53 P E E energy (J) P Power (W) t Time (sec) t How much energy is used by a 1200 W hair dryer running for 5 minutes?

54 P E E energy (J) P Power (W) t Time (sec) t How much energy is used by a 1200 W hair dryer running for 5 minutes? 5 minutes x 60 = 300 s E= P x t E = 1200 x 300 E = J

55 If a hairdryer running for 5 min can use J, the amount of energy used in your home in 1 day must be very large. To measure larger values, use the unit kilowatt hours kw h 1J = 1W x1s 1 kw h = 1000W x 3600 s 1 kw h = J

56 A 1600 W appliance is used for 15 min. How much energy, in kw h, are used?

57 A 1600 W appliance is used for 15min. How much energy, in kw h, are used? P= 1600 W = 1.6 kw t= 15 min = 0.25 hr E = P x t E = 1.6 x 0.25 = 0.4 kw h

58 Efficiency: The percentage of energy input that is converted to a useful output Example: Light bulb the amount of energy put in compared to the light given off

59 Calculating Efficiency Efficiency= useful energy output x 100 total energy input

60 Calculating Efficiency Efficiency= useful energy output x 100 total energy input Example: How efficient is an incandescent bulb if it uses J to provide J of light energy?

61 Calculating Efficiency Efficiency= useful energy output x 100 total energy input Example: How efficient is an incandescent bulb if it uses J to provide J of light energy? x 100 = 60 %

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