Lesson 6


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Learn about electricity, circuits,

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Lesson 6

  1. 1. Lesson 6: Electricity Technology 3º ESO
  2. 2. Index         What is electricity Electrical magnitudes Ohms law Measuring with a multimeter Electric circuits: Elements Electric symbols Types of circuits Electric machines
  3. 3. What is electricity?     Electricity is a form of energy It has its origin in the electrical charges existing in the atoms (electrons and protons), which strongly interact Electricity can be natural, such as ligthning or artificial (electric circuits) As a form of energy, it is easy to produce and transform. Index
  4. 4. ELECTRIC MAGNITUDES Magnitude Definition Units Expression Voltage, (tension) Energy given to the charges to move them V (volts) V=I·R Resistance Difficulty to be passed by electricity Ω(ohm) R= ρ·l/s2 Intensity Charge passing through a conductor in a second A (amp) I=Q / t(s) Power Energy produced (or lost) by the current in a time unit W (watt) P=V·I PL=R·I2 Index
  5. 5. Ohm’s law  Ohm’s law says that the tension is equal to the product of the intensity and the resistance V=R·I  This is equivalent to: I=V/R ↔R=V/I Index
  6. 6. Electric circuits and their elements An electric circuit is a closed path where the charges flow between to points with different electric tension  We use electric circuits to transport and transform energy  An electric circuits needs at least 1. A power supply 2. A conductor 3. A receiver It is also important to include control elements  Index
  7. 7. Power suppliers   1. 2. A power supply gives energy to the charges so that they flow trough the circuit There are different types of suppliers Chemical: batteries DC Mechanical: dynamos DC and alternators AC
  8. 8. Conductors   A conductor is an element where the charges flow without a significant resistance They are normally wires: several long and thin copper (or aluminum) conductors covered by an insulating plastic layer
  9. 9. Receivers  1. 2. 3. 4. 5. Receivers transform electricity into a useful form of energy so that we make the circuit profitable. They can convert electricity into: Ligth: lamps Movement: motors Heat: resistances Sound: speakers etc
  10. 10. Control elements  Control elements let us stop or allow the flow of charges (switch) or change the way of the electricity through the circuit (conmuter) Index
  11. 11. Electric symbols   An electric symbol is a picture which represents a circuit or an element of it They make it easier to represent and understand circuits Index
  12. 12. Electric machines  Many essential devices work or help us to control electricity  Transformer  Motor  Dynamos or alternators  Relay Index
  13. 13. Transformers Transformers change (raise or lower the) tension of the alternating current They are formed by a square core with two coils (copper wires), primary (N1 turns , V1 and I1) and the secondary. The alternating current induces a magnetic flux wich travels trough the iron core and induces a current I2 with a voltage V2 in the secondary coil of N2 turns. This equations are satisfied P1=P2 ↔ V1·I1=V2·I2 V1/N1=V2/N2 ↔ V1·N2=V2·N1 I1·N1=I2·N2
  14. 14. Motors  Motors can be AC or DC. They are both based on magnetic fields. A current flows trough a coil in the rotor / stator. The stator / rotor is a magnet. Due to the variation of the magnetic field flow caused by the electric current
  15. 15. Dynamos / alternators  Dynamos (DC) or alternators (AC) are like motors which generate DC or AC current when the rotor is moved inside the stator. The variation of the magnetic field due to the rotation of a magnet induces an electric current in the stator.
  16. 16. Relays      1. 2. A Relay is a swith controlled by an electromagnet. An electromagnet is a coiled conductor wire where the current flows creating a magnetic field. The magnetic field makes the swith change its position due to magnetic atraction When current stops, the magnetic field dissapears and the switch returns to its original position due to a spring. Relays have two independent circuits: the control circuit: Activates the electromagnet The power circuit, which is controlled by the switch Index