chapter 11: current electricity. current electricity to operate electrical devices, you need a...

Download Chapter 11: Current Electricity. Current Electricity To operate electrical devices, you need a steady flow of electrons. Unlike static electricity, a

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  • Slide 1
  • Chapter 11: Current Electricity
  • Slide 2
  • Current Electricity To operate electrical devices, you need a steady flow of electrons. Unlike static electricity, a flow of electrons move continuously as long as 2 conditions are met. 1.The flow of electrons requires an energy source 2.The electrons will not flow unless they have a complete path to flow through (electrical circuit) Current electricity is the continuous flow of electrons in a circuit.
  • Slide 3
  • Electric Circuits An electric circuit must include: 1.An energy source 2.A conducting wire 3.A load which is a device that converts electrical energy to another form of energy; ex. Light bulb Many electric circuits also include a switch that turns the circuit on or off by closing or opening the circuit.
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  • Electric Current Electric Current is the measure of the rate of electron flow past a given point in a circuit; measured in amperes (A).
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  • Examples of Loads Converts electricity to light bulblight or heat energy fanmechanical energy doorbellsound energy
  • Slide 6
  • Electric Current, cont Think of it in terms of a waterfall. If you could count the number of water molecules that drop over the edge every second, you could get the rate at which water is flowing past a particular point. Now think of the water molecules as electrons in a wire running past a particular point in a specific amount of time and you have the concept of current.
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  • Measuring Current Current in a circuit is measured using an ammeter. The unit of electric current is the ampere (A). An ampere is a measure of the amount of charge moving past a point in the circuit every second.
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  • Measuring Current, cont One ampere of charge in a circuit means that 6.2 x 10 18 electrons pass a particular point every second.
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  • Measuring Current, cont When you connect an ammeter or voltmeter to a circuit, they must be on the right terminals. There are two terminals on a meter that you use to connect to a circuit. The negative () terminal is often black, The positive (+) terminal is often red.
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  • Measuring Current, cont Always connect the positive terminal of the meter to the positive terminal of the electrical source. Connect the negative terminal of the meter to the negative terminal of the electrical source.
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  • Calculating Current I Q t
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  • QuantitySymbol Units of measurement ChargeQC (coulomb) CurrentI A (amperes) amps Timets (seconds) Calculating Current, cont
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  • I Q t Rearranging formulas - The magic triangle Therefore, 1 Ampere = 1 Coulomb / s Calculating Current, cont
  • Slide 14
  • Sample Question 1 If 310 C of charge passes a point in a conductor in 10 minutes, what is the current through that point in the conductor? Use GRASP and sig. digits.
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  • Sample Question 2 A 6.5 amp vacuum cleaner is used for 34 minutes, how much charge would pass through the vacuum during this time? Use GRASP and sig. digits.
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  • Sample Question 3 A 5.3 amp drill has 20 coulombs of charge pass through it, how long was the drill used for? Use GRASP and sig. digits.
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  • Potential Difference Example: An apple hanging from a low. The apple has potential energy because of its position above the ground. If the apple falls down, it will convert its stored energy, or potential energy, into motion. Suppose an apple at a higher branch. It would have even more potential energy to convert. Each electron has electric potential energy. Potential energy is the energy stored in an object.
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  • Potential Difference, cont A battery has chemical potential energy in the electrolyte in its electrochemical cells. The chemicals in the electrolyte react with the electrodes. This causes a difference in the amount of electrons between the two terminals.
  • Slide 19
  • Potential Difference, cont One terminal in a battery has mainly negative charges (electrons). The other terminal has mainly positive charges. The negative charges are electrons, which can move, are attracted to the positive charges at the positive terminal.
  • Slide 20
  • Potential Difference, cont If a conductor, such as a copper wire, is connected to both terminals, then the electrons flow from the negative terminal to the positive terminal. The difference in electric potential energy between two points in a circuit is called the potential difference or voltage (V).
  • Slide 21
  • Potential Difference, cont This difference causes current to flow in a closed circuit. The higher the potential difference in a circuit, the greater the potential energy of each electron.
  • Slide 22
  • Measuring Potential Difference The potential difference between two locations in a circuit is measured with a voltmeter.
  • Slide 23
  • Measuring Potential Difference, cont Example: Connecting wires from a negative terminal on a battery across a voltmeter and then back to the positive terminal. The voltmeter would then display the potential difference of the battery. The SI unit for measuring potential difference is the volt (V).
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  • Measuring Potential Difference, cont A voltmeter must be connected in parallel with a load in the circuit in order to compare the potential before and after the load.
  • Slide 25
  • Electrochemical Cells Batteries A battery is a combination of electrochemical cells. Each electrochemical cell is a package of chemicals that converts chemical energy into electrical energy that is stored in charged particles. A simple electrochemical cell includes an electrolyte and two electrodes.
  • Slide 26
  • Electrochemical Cells Batteries; cont An electrolyte is a liquid or paste that conducts electricity because it contains chemicals that form ions. An ion is an atom or a group of atoms that has become electrically charged by losing or gaining electrons. Sulphuric acid is an example of an electrolyte.
  • Slide 27
  • Electrochemical Cells Batteries; cont Electrodes are metal strips that react with the electrolyte. Two different electrodes, such as zinc and copper, are used in a battery. The electrodes and electrolyte react causing one electrode to collect and the other to lose electrons.
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  • Wet Cells and Dry Cells An electrochemical cell that has a liquid electrolyte is called a wet cell. Wet cells are often used as an energy source for cars and other motorized vehicles.
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  • Wet Cells and Dry Cells, cont An electrochemical cell that uses a paste instead of a liquid electrolyte is called a dry cell. Dry cells are used in flashlights, hand-held video game devices, cameras, and watches. Each electrode in a dry cell or battery can also be called a terminal. Terminals are the end points in a cell or battery where we make a connection
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  • Fuel Cells A fuel cell is an electrochemical cell that generates electricity directly from a chemical reaction with a fuel, such as hydrogen. Fuel cells are used in electric vehicles. The cell is not used up like an ordinary cell would be because as the electricity is produced, more fuel is added.
  • Slide 31
  • Homework Read 434-438 Complete #1-4, page 436 and #1-5, page 438
  • Slide 32
  • Recall. Electric current can be thought of as the number of electric charges (electrons) passing a point in the circuit per second. Can also be thought of as a speed of electron flow.
  • Slide 33
  • Electric Potential (Voltage) Voltage can be thought of as the energy that each electron in the circuit contains. Electric potential refers to the amount of energy that electrons possess in a circuit.
  • Slide 34
  • Electric Potential, cont A load (ex. light bulb) converts electrical energy into another form of energy (ex. light energy and heat energy). You can compare this to the water flowing past a water wheel. The wheel converts some of the energy of the water into motion. The water has more energy before the wheel than after the wheel. Therefore, there is higher voltage before the load than after the load.
  • Slide 35
  • Calculating Electric Potential (Voltage) The electrical potential energy for each coulomb of charge in a circuit is called the electric potential (V) aka voltage. V E Q
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  • Calculating Potential Difference (Voltage), con`t QuantitySymbol Units of measurement ChargeQC (coulomb) EnergyEJ (Joules) VoltageVV (Volts)
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  • Where E is the energy required to increase the electric potential (V) of a charge, Q. Potential difference is often called voltage. Calculating Potential Difference (Voltage), con`t and the formula can be rearranged Energy Charge V E Q
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  • Calculating Potential Difference (Voltage), con`t Therefore: One volt (V) is the electric potential difference between two points if one joule of work (J) is required to move one coulomb (C) of charge between the points. Volts = Joules Coulombs
  • Slide 39
  • Sam