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Current Electricity

Current Electricity. Current Electricity. The movement of electric charge from one place to another. Voltage. Potential (Voltage)- IS THE ELECTRIC POTENTIAL PER CHARGE MOVING BETWEEN TERMINALS. THIS IS LIKE THE ELECTRIC PRESSURE PUSHING THE ELECTRONS.

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Current Electricity

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  1. Current Electricity

  2. Current Electricity • The movement of electric charge from one place to another.

  3. Voltage • Potential (Voltage)- • IS THE ELECTRIC POTENTIAL PER CHARGE MOVING BETWEEN TERMINALS. • THIS IS LIKE THE ELECTRIC PRESSURE PUSHING THE ELECTRONS. • VOLTAGE DOES NOT MOVE, IT PUSHES THE ELECTRONS. http://faraday.physics.utoronto.ca/IYearLab/Intros/DCI/Flash/WaterAnalogy.html

  4. High Voltage Low Voltage

  5. High Voltage Low Voltage

  6. Voltage • Potential (Voltage) cont’d- • Measured in volts (V) • Measured using a voltmeter.

  7. Current • Current- • The measure of the rate at which electric charges move past a given point in a circuit. • Measures the amount of electricity passing a point. • Measured in amperes (A) • Measured using an: • Ammeter- larger currents • Galvanometer- smaller currents

  8. High Current Low Current

  9. High Current Low Current

  10. Resistance • Resistance • The measure of an objects opposition to the passage of a steady electrical current • Measured in ohm’s (Ω) • Measured using an ohmmeter

  11. Low Resistance Low Resistance High Resistance

  12. Ohm’s law • Created by Georg Ohm (1789- 1854) • “the potential difference between two points on a conductor is directly related to the electric current flowing through the conductor” Potential difference= Electric current x electrical resistance V = I x R

  13. Example One • What is the voltage drop across a tungsten filament in a 100-W light bulb? The resistance of the filament is 144 Ω and a current of 0.833 A is flowing through it.

  14. Example Two • An electric toaster is connected to a 120-V outlet in the kitchen. If the heating element in the toaster has a resistance of 14 Ω, calculate the current flowing through it.

  15. Problem solving ? Textbook (10-10)

  16. Electrical circuits • Electrical circuit- • Controlled path of flowing electricity in a complete circle • Contain 4 parts • Source- Where electricity comes from. • Load- Where the electrical energy is transferred. • Control- What starts and stops the electricity. • Connectors- The path where the electricity runs.

  17. Load Source Control Connector

  18. Electrical circuit- Source • Cells- Converts chemical energy into electrical energy. • Batteries- combination of 2 or more cells • Generators-a device that converts movement into electrical energy • Photoelectric cells- a cell that converts light directly into electrical energy

  19. Cell Battery Generator Photoelectric Cell

  20. Electrical circuit- Source cont’dCells • Primary cells- Disposable cells • Secondary cell- reusable cells All cells contain: Electrodes- Metal plates that are placed in the electrolyte Electrolytes- Chemicals that conduct electric current Positive terminal- Place where positive charges collect Negative terminal- Place where negative charges collect

  21. Electrical Sources • Cells can be: • Wet cells- electrolyte is a liquid • Easy to make with available chemicals • Hard to transport and quite large Electrodes Electrolyte

  22. Electrical Sources • Dry cells- Electrolyte is a paste • Easy to transport and very compact • Special and sometimes more dangerous chemicals are required.

  23. Electric circuit- Load • Anything that converts electrical energy into the form of energy required • Light bulb (light energy) • Toaster (heat energy) • Television (light and sound energy) • Computer (light and sound energy) • Fan (mechanical energy) • Music player (sound energy) • Motor (mechanical energy)

  24. Electrical circuits- Control • A device that controls the flow of electrical energy • Switches • Single pole switches • Double pole switches • 3-way switches • Buttons • Keys • Timers • Bimetallic strips • Variable resistors (dimmer switches)

  25. Electrical circuits-Connectors • A conducting wire that provides a controlled path for electric current to flow to each part of the circuit • Conductor- A substance where electrons can move freely from one atom to another. (electric current) • Insulator- A substance where electrons cannot move freely from one atom to another. (Static electricity) • Superconductor- Ceramics that conduct electricity with no resistance at low temperatures. (bullet trains)

  26. Conductor e e e e Insulator e e e e e Superconductor e e e e

  27. Electrical circuits • Open circuit- circuit is not connected, switch is open, no electricity is flowing • Closed circuit- circuit is connected, switch is closed, electricity is flowing • Short Circuit- Circuit where there is not a load attached to the circuit, no resistance. Can be very dangerous, connectors can become overheated and burn, cells will use up the potential very rapidly.

  28. Open Circuit Closed Circuit

  29. Short Circuit

  30. Electrical circuits • Electrical circuits can be made in two different ways. • Series circuit- One path of electric charge

  31. Electrical circuits • Parallel circuit- 2 or more paths for electric charge to follow (branches)

  32. Electrical circuits(10-7) • Connecting cells in: • Series- the potentials of the cells are added together • ie. Three 1.5V cells connected end to end has a potential of 4.5V + + + - - - = 4.5 V

  33. Electrical Circuits • Parallel- the cells will last longer • Potential remains the same + + + - - - = 1.5V

  34. Electrical circuits • Connecting loads in: • Series- • Circuit potential remains the same • (total) Resistance is additive • Circuits current changes according to Ohm’s law

  35. V= 1.5V R= 3Ω + 4Ω = 7Ω I = ? 3 Ω 1.5V V = I x R I = V/R 4 Ω I = 1.5V/ 7Ω I = 0.21 A

  36. V= 1.5V R= 5Ω + 7Ω = 12Ω I = ? 5 Ω 1.5V V = I x R I = V/R 7 Ω I = 1.5V/ 12Ω I = 0.14 A

  37. Electrical circuits • Parallel- • Circuits potential remains the same • (total) Resistance decreases • Circuits current increases according to Ohm’s law

  38. Electrical circuits • Pro’s and cons of series and parallel circuits. • Series • Pro’s • Simple to make and easy to follow. • Con’s • Limited control over the circuit and when one load is broken, the entire circuit won’t work.

  39. Electrical circuits • Pro’s and cons of series and parallel circuits. • Parallel • Pro’s • Lots of control over the circuit and not all loads have to be working at the same time • Con’s • Much more complex and difficult to follow.

  40. Multimeter • A multimeter is a device that can measure potential, current and resistance in one machine. • When using a multimeter in a circuit, it must be connected properly to get a correct reading • When using as a voltmeter or ohmmeter, it must be connected in parallel to the circuit • When used as an ammeter, it must be connected in a series in the circuit

  41. Voltmetre or ohmmetre -Connect in parallel Multimetre Ammetre -Connect in series Multimetre

  42. Circuit schematics • Schematic circuit diagrams are used to show how electrical circuits are connected on paper. • Special symbols are used to indicate the different parts of the circuit.

  43. - Voltmeter - Cell V - Battery (2 cells) - Ammeter A - Light - Switch (1 pole) - Motor M

  44. Making a Circuit Schematic Diagram • Create a circuit that has one cell powering 1 light that is controlled by a switch.

  45. Create a circuit with a 3 cell battery that has 2 lights connected in series all controlled by one switch.

  46. Create a circuit with a 3 cell battery that has 2 lights connected in parallel all controlled by one switch, with another switch controlling just one of the lights.

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