Energy

• Atoms


  Tiny particles that everything around us is made up of
• Subatomic particles that make up atoms

  • Protons
  • Neutrons
  • Electrons
• Protons


  • Found in the nucleus, have a positive charge
• Neutrons


  • Found in the nucleus, have no charge - they are neutral
• Electrons


  • Move around the nucleus in a space called the electron shell, have a negative charge
• Usually an atom has an equal number of protons and electrons, therefore the charges cancel each other out and the atom has no overall charge
• Electricity


  A form of kinetic energy that is produced by moving electrons
• Insulators


  Substances that electrons cannot flow freely through (e.g. plastic, rubber, wood)
• Conductors


  Materials that allow both heat and electrical energy to flow through them (e.g. steel, aluminium, other metals)
• How electricity works


  1. Electron breaks free from an atom

  2. Attaches to a new atom

  3. This atom ejects one of its own electrons

  4. This electron looks for another atom to attach to

  5. This motion of electrons creates a flow, which is electricity
• Circuit


  An unbroken loop of conduction material that allows electricity to flow continuously without a beginning or end
• Components of a circuit


  • Energy source (e.g. battery, cell)
  • Conductive path (e.g. wires)
  • Load to use the electricity (e.g. lightbulb, fridge, TV)
• Voltage (potential difference)


  A measure of the force that pushes electric charge (electrons) through a circuit, the difference in electrical potential between two points
• Current


  The amount/size of electric charges (electrons) that flow through a circuit, flows from high voltage to low voltage
• Resistance


  The measure of opposition to current flow in an electrical circuit, determines how easily or difficulty electric charges can move through a circuit
• Ohm's Law


  1. V = I x R

  2. I = V/R

  3. R = V/I
• Ohm's Law states that the current flowing through a circuit is directly proportional to the voltage applied and inversely proportional to the resistance
• Circuit Symbol for a Cell

  
• Circuit Symbol for a Battery

  
• Circuit Symbol for a Open Switch

  
• Circuit Symbol for a Closed Switch

  
• Circuit Symbol for a Lamp

  
• Circuit Symbol for an Ammeter

  
• Circuit Symbol for a Voltmeter

  
• Series Circuit

  
• Parallel Circuit

  
• Series Circuits


  • Circuits connected in series have switches that operate in an all-or nothing manner (all off or all on)
  • If one light bulb blows/breaks in the circuit, then all of the light bulbs turn off
• Series Circuit


  1. Total voltage is shared among the globes

  2. Each component receives a equal fraction of the total voltage

  3. Total current flows through all of the light bulbs

  4. Total current flows through only one path

  5. Each component receives the total current
• Adding extra light bulbs in a series circuit

  • Increases the resistance
  • Each light bulb may also appear dimmer as the resistance is increased
• Parallel Circuits


  • Circuits connected in parallel have a switch that operates in a selective manner
  • If a switch is placed on a parallel path, only one light bulb will be affected
  • Separate switches can be used to operate light bulbs independently
  • If one light bulb blows/breaks, the other light bulbs will still work
• Parallel Circuit


  1. Each light bulb receives the total voltage

  2. Light bulbs will not decrease in brightness with each additional light bulb added

  3. Total current splits into different paths and is divided among the light bulbs

  4. Each light bulb will receive a equal fraction of the total current
• Adding extra light bulbs in a parallel circuit

  • Does not increase the resistance as the light bulbs are on different paths
  • Each additional light bulb will not appear dimmer at the resistance does not increase
• Resistance (R): The opposition offered by a material or device to the flow of electricity, measured in ohms.
• Current (I): The rate at which electric charges flow through a conductor, measured in amperes.
• Voltage (V): The difference in electrical potential energy per unit charge between two points, measured in volts.
• Efficiency


  A measure of how much useful energy a device outputs compared to the total energy that goes in
• Light bulb efficiency


  • 100J electrical energy in, 25J useful light energy out = 0.25 (25%) efficiency
• Efficient CFL light bulb

  Wastes less energy than a filament bulb
• Same energy input to both light bulbs


  More efficient device gives more useful light energy out
• Cost of electricity


  Depends on time used, power of device, and cost per kWh of electricity