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# Electricity and Electrical Circuits

Electricity and Electrical Circuits. We are now moving on to ?current electricity".Current electricity is the flow of electrons through a medium such as wires.Current electricity always wants to travel to the earth. (Think back to induction to understand why)Electricity is lazy, it will always ta

## Electricity and Electrical Circuits

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1. Electricity and Electrical Circuits Once again… Electricity is the flow of ELECTRONS!! Up until now we have been dealing with static electricity (it is called static because it is held in a single location)

2. Electricity and Electrical Circuits We are now moving on to “current electricity”. Current electricity is the flow of electrons through a medium such as wires. Current electricity always wants to travel to the earth. (Think back to induction to understand why) Electricity is lazy, it will always take the shortest, easiest route to its destination. (Think back to insulators and conductors, which would make an “easy” path?)

3. Electrical Current There are two important factors in electrical current The number of electrons released into the medium The amount of energy each electron carries with it after it is released

4. Circuit Diagrams Current conventions: We will be using the electron flow convention Electrons leave the negative terminal and flow to the positive terminal of the cell Know it, live it, write it on tests!

5. Analogy Time Read pages 300-303 Answer questions #1-3 (301) and #1 (303) Make some notes on the parts of electrical circuits, electrical circuit diagrams and electric potential. Be sure to define the key words Current, circuit, load, source/cell, closed circuit, open circuit, control device, potential, volt and voltage. Create your own analogy (other then the water wheel one) to relate the flow of energy in a circuit to others. Be prepared to share/present your answer.

6. Work for Today Read pages 310-311 Answer questions #2&3 Make notes on series and parallel formations of circuits Incorporate this information into your analogy Be prepared, we will be sharing analogies before moving on.

7. Drawing circuit diagrams

8. Note: That was the simplified version

9. Notes on circuits Be sure you are clear on the direction of electron movement in the circuit. Be sure you know the symbols, what they represent and how they work/react in different situations Know the differences between parallel and series circuit set ups

10. Notes on circuits Whatever the voltage is coming out of the battery (cell) will be used up by the resistors or loads in the circuit. As such the voltage at the positive end of the circuit is always zero relative to the negative end

11. Drawing circuit diagrams Called “schematic circuit diagrams” Connecting wires are usually drawn as straight lines (that means with rulers) and at right angled corners. Symbols are simple and usually look similar to what is happening

12. Parts of an Electric Circuit The source: The producer of electrical energy. Examples? Nuclear power stations, cells, batteries, portable generators An electrical load: Anything that converts electrical energy into the form of energy required. Examples? Toaster, light bulb, microwave, fan, etc.

13. Parts Cont’d Electric Circuit Control Device: the object that controls electric circuits Examples? Light switches, on/off buttons and microwave timers Connectors: A conducting wire that provides a controlled path for electric current to flow to each part of the circuit. Examples? Transmission live wires, electric cables

14. Open vs. Closed Circuits What do you think this means? A circuit can be described as either open or closed Closed circuit: the circuit is operating and the current is flowing. The switch is “on”. Open circuit: The circuit is NOT operating. The switch is “off”

15. In order for circuit to work there MUST be a continuous unbroken chain of electrons moving from the negative terminal of the dry cell to the positive terminal of the dry cell Therefore, the circuit must be closed.

16. Circuit Diagrams

17. Steps to follow when drawing schematic circuit diagrams Figure out what the components of the circuit is going to be. Recall what symbols correspond to each circuit component Arrange the components in order they would appear in a functioning circuit Connect the parts of your circuit using straight lines (USE A RULER!) * Remember straight lines represent connecting wires. Connecting wires should be at right angles (90 degrees).

18. Sample Circuit diagram

20. Voltmeters and Ammeters Review page 546 on the use and reading of voltmeters and ammeters. A voltmeter MUST be hooked up in parallel with the component being investigated An ammeter MUST be hooked up in series to measure current

21. Voltmeters and Ammeters A voltmeter MUST be hooked up in parallel with the component being investigated An ammeter MUST be hooked up in series to measure current Incase you forgot Series means only a single path for electrons to flow Parallel means multiple paths for electrons to flow

22. Practice Draw the following circuits - Two cells in series - Three lights in parallel - A switch that operates two lights only - Three lights in series - Two motors in series - A switch that operates the motors only - Two lights in series - Three resistors in parallel - A switch that will control both lights and one resistor

23. What to do … Read pages 314 – 319 Be sure to note: Definitions Units Equations NOTE: From now on, we will consider current and electron flow to travel in the SAME direction.

24. Ohm’s Law The following information is also available to you on page 317 of your textbook Ohm’s Law states: The potential difference between two points on a conductor is proportional (directly related) to the electric current flowing through the conductor.

25. Ohm’s Law From Ohm’s law we get the mathematical equation to calculate parts of electricity V = I x R V ? Is the potential difference or “voltage drop” I ? is the electric current in the circuit R ? is the electrical resistance

26. Practice ohms law A hair dryer has a resistance of approximately 50O. If the hair dryer is hooked to a typical 120V wall outlet, what is the current in the circuit? If I replaced the hair dryer with a dryer of resistance 500 O, how would this affect the current?

27. The GUESSS Method How to solve problems using GUESSS G – Write down what information you were "GIVEN" in the question U – Write down what information you need but is still "UNKNOWN" to you. (This is what you are trying to find in the question) E – Write down the EQUATION(s) you will use to solve the problem S – SUBSTITUTE all your known variables into your equations in the appropriate place S – SOLVE the problem for your unknowns S – Make a STATEMENT about your solution

28. Practice ohms law An Xbox 360 is plugged into a typical 120V wall socket. The current found running through the game system is found to be 11.4 A. A Playstation 3 is also plugged into a wall socket and found to have a current of 10.8 A. Which system has the greater electrical resistance, and how much greater is it? Which system will use electricity more quickly? Which system is more likely to overheat? Give a reason for your answer.

29. Review of grade nine again Ohm’s Law R = V / I R ? Resistance measured in ohms (O) V ? Electrical potential difference in volts (V) I ? Electrical current in Amperes (A) 1 O = 1 V/A Electrons are lazy, they will take the path of least resistance. Short circuits are situations where the electrons are allowed to flow around the circuit without a load (thus they return to the cell without losing voltage)

30. Kirchhoff’s Laws Both series and parallel circuits have triad (three) rules that apply to them These three rules apply specifically to that type of circuit (and NOT the other!) Each of the three rules corresponds to a single component of the ohms law equation: One rule applies to resistance (R) One rule applies to current (I) One rule applies to voltage (V)

31. Loads In Series Circuits Laws of series circuits: the supply voltage is equal to the sum of the individual voltage drops Vt = V1 + V2 + V3 + V4… + V8 the amount of current is the same through any component in the circuit It = I1 = I2 = I3 = I4 … = I8 the total resistance of any series circuit is equal to the sum of the individual resistances Rtotal = R1 + R2 + R3 +…..+ R8

32. Loads In Parallel Circuits Rules of parallel circuits: the voltage is equal across all components in the circuit Vt = V1 = V2 = V3 = V4 … = V8 the total circuit current is equal to the sum of the individual branch currents It = I1 + I2 + I3 + I4 … + I8

33. Cells in series When connecting cells in series several things occur The energy each electron receives is increased as it passes through each battery The total number of electrons drawn into the circuit remains the same The Laws Vt = V1 + V2 + V3 + V4 … + V8 It = I1 = I2 = I3 = I4 … = I8

34. Cells in parallel When connecting cells in parallel several things occur The energy each electron receives is unchanged as they pass through only a single cell The total number of electrons drawn into the circuit is increased with each cell added as the same number of electrons are drawn from each The Laws Vt = V1 = V2 = V3 = V4 … = V8 It = I1 + I2 + I3 + I4 … + I8

35. Analyzing a circuit Can be done relatively easily using Ohm’s law and the three rules for each type of circuit Apply the rules to get unknowns at various locations Use ohms law at any location where you have two known values Check results using rules

36. Analyzing a circuit The best method for analyzing is to make a table…

39. Multiple Cells

40. Summary Of Ciruits

41. Energy Electrical energy is the amount of energy transferred to an load by moving charges. This means that electrical energy is the energy given to a load by electrons moving through it. This energy is converted by load to another form.

42. Energy Energy is measured in units called “joules” represented by the letter J Energy is ALSO measured in units called kilowatt hours (kWh). These are used because a joule is such a small unit of measurement. To give you an idea 1 kWh = 3600000 J

43. Energy Energy is calculated using V, I, ?t Because there are four variables you cannot use a magic triangle The equation we are stuck with is V x I x ?t = E V ? Voltage drop in volts I ? Current in amperes ?t ? Amount of time elapsed in seconds E ? Electrical energy measured in joules

44. Energy Notes: The J is the same type of measurement as kWh Volts x Amps = Watts 1000 Watts = 1 kW 3600 s = 1 hour 3600000 J = 1 kWh See page 335 for more information Complete questions 1 – 3 on 336

45. Energy Efficiency The energy efficiency of an electrical device is determined by how much of the electrical energy that enters that object is converted in the form that is desired (heat, light etc.) The more electrical energy that enters a device and is converted to the proper form, the more efficient that device is

46. Efficiency Energy Efficiency is calculated by... Eefficiency = Eout / Ein x 100% Hence the more energy output from the device the higher its efficency. NOTE: The input is constant and will be based on the attached source.

47. Power Power is the amount of energy that passes through a circuit in a given amount of time. More energy and faster movement result in greater power

48. Power Power has two equations, both of which can be used in magic triangle form P = E / ?t AND P = V x I

49. Power Power has the unit Watts (W) which is often converted to kW to better apply the numbers to real life. 1000 W = 1 kW Complete questions 1 – 3 on page 339

50. Efficient Energy Use To calculate how much of the electricity an appliance receives is converted into the useful form we want we use the following equation… % Efficiency = [Energy Output (in J or kWh) ÷ Energy Input (in J or kWh)] x 100%

51. Efficient Energy Use % Efficiency = [Energy Output (in J or kWh) ÷ Energy Input (in J or kWh)] x 100% Energy output is the amount of energy released by the appliance or device in a USEFUL form. (This would be the form we want it in) Energy input is the total amount of energy entering the appliance or device this would be the electrical energy being supplied from a cell or wall socket %efficiency is the percentage of energy entering the device that is then changed to a useful form. It has NO UNITS! It is a percentage only. The energy which does not become a useful form is lost as heat, light or both.

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