Science 9 Physics

• Voltage


  Electrical potential difference in volts (V)
• Loads


  • Can be connected in series or in parallel in a circuit
• Ohm's Law


  V = IR
• V


  Electrical potential difference (voltage) in volts (V)
• Types of circuits


  • Series circuit
  • Parallel circuit
• Series circuit


  A circuit in which current can only flow along one path
• Parallel circuit


  A circuit that has at least one branch point where the current splits into two or more pathways
• Series circuits are impractical for homes
• Loads connected in series in a kitchen

  • If one load (ceiling lamp) burns out:
  • The circuit will be open
  • Charges stop moving
  • No loads (microwave, toaster) in the circuit will work
• Parallel circuits are practical because each appliance is controlled by its own switch without shutting off others
• Parallel circuit in a home

  • All of the appliances are running
  • A large amount of current is passing through the conductor wire (arrow)
  • The ceiling lamp and microwave are turned off, but the toaster and radio are still running
• When large amounts of current flow through a wire, it can overheat and start a fire
• Many separate parallel circuits are installed in buildings
• A large electrical cable carrying electrical energy branches out and is connected to each parallel circuit in a circuit panel
• Chemical energy


  Separates electrical charges in cells
• Charges


  Can flow through conductors, but not insulators
• Moving electrical charges


  Form an electric current
• Load


  Resists the flow of current
• Conductors


  Must form a closed loop to allow current to flow
• Electrochemical cell


  Transforms chemical energy into electrical energy
• Electrochemical cell


  • An AA "battery" is an electrochemical cell (even though it is commonly known as a "battery")
• Electrochemical cell


  1. Chemical reactions of two different metals or metal compounds occur on the surface of electrodes

  2. Electrodes are in a solution called an electrolyte

  3. The chemical reactions cause one electrode to become positively charged, and the other to become negatively charged

  4. The electrodes are in contact with terminals in the cell

  5. When the terminals are connected to an electrical pathway, charges flow through
• Battery


  A connection of two or more electrochemical cells
• Electrochemical cells and batteries


  Sources (anything that supplies electrical energy)
• How an electrochemical cell becomes "charged"

  1. The worker (chemical energy) carries negative charges (electrons) up a ladder and places them at the negative terminal of the cell

  2. The worker leaves positive charges on the bottom at the positive terminal

  3. The first electron is easy to carry up, since one only pair of charges is being separated

  4. Only a small amount of electrical energy is stored in the cell

  5. After a few charges have been separated, the attraction between the positive charges at the positive terminal and the negative charge of the electron being carried increases

  6. The negative charges of the electrons at the negative terminal are repelling the negative charge of the electron being carried

  7. Therefore, it takes more energy to carry each additional electron

  8. The worker (chemical energy) has done a lot of work to separate the charges

  9. This energy is stored in the electrical potential energy of the separated charged

  10. Eventually, repulsion of the electron by the negative charges at the negative terminal and the attraction by the positive charges gets so strong that the worker cannot carry any more electrons

  11. No more chemical energy will be transformed into electrical potential energy

  12. The battery is now charged
• Electrical potential difference


  A quantity that provides a measure of the electrical potential energy a unit of charge gains when passing through a source
• Voltage


  Symbol: V, Units: volts (V)
• Electrical potential difference


  Measures the difference in electrical potential energy per unit of charge between the positive terminal and the negative terminal in an electrochemical cell
• 1.5V cell


  It took 1.5 units of energy to separate the last unit of charge (e.g., carry the last unit of charge "up the ladder")
• Rubbing two different solid materials together

  1. Electrons can be transferred from one material to the other

  2. Electrons with either stay on the surface of the new material or travel through it
• Insulator


  A material charges cannot travel through
• Conductor


  A material charges can travel through
• Conductivity


  An indication of how easily charges travel through a material
• Electrons can move through almost all metals (conductors); can move through some metals more easily than others
• The higher the conductivity of a material, the more easily electrons can move through
• Chemical energy from a source (cell or battery)


  Causes charges to move through a conductor (wires), carrying energy to an electrical device (cellphone)
• Moving charges


  An electric current
• Current


  Measured in amperes: A
• Load


  A device that converts electrical energy into another form of energy
• Load


  • Light bulb: A load that transforms electrical energy into light energy
  • Radio: A load that transforms electrical energy into sound energy