Science Revision

• Atom


  Smallest part of matter

  
• Nucleus


  has a positive charge; center of the atom; contains protons and neutrons

  
• Proton


  Positively charged subatomic particle. Found in the nucleus of the atom.

  
• Electron


  Negatively charged subatomic particle. Found outside of the nucleus in energy levels. Smallest particle...

  
• Neutron


  Neutrally charged subatomic particle. Found inside the nucleus of the atom.

  
• Energy Cloud / Energy Level


  Space outside the nucleus where electrons orbit.

  
• Neutral


  an atom that has an equal number of protons and electrons

  
• Valence Electron


  The electrons in the outer most level. Used in bonding with other atoms.

  
• Subatomic Particles


  The small parts that make up the atom. Protons, electrons, and neutrons.

  
• Atomic Number


  Number of protons in the nucleus of an atom.

  
• Atomic Mass


  Number of protons and neutrons in an atom.

  
• Atomic Mass Unit


  A unit of mass that describes the mass of an atom or molecule.

  
• Bohr Model


  model of the atom in which electrons move rapidly around the nucleus in paths called orbits

  
• Reactivity


  How readily a substance combines chemically with other substances.

  
• Physical Property


  A characteristic of a pure substance that can be observed without changing it into another substance.

  
• What is the National Grid?

  - the national grid is the network of high-voltage power lines between major power stations

  - it distributes electricity from power stations to consumers
• Voltage in homes


  230V
• Voltage in transmission cables

  400,000V
• Transformer


  used to change P.D on the national grid
• Step-up transformer


  - used just after the power station

  - increases voltage

  - decrease current
• Step-down transformer


  - used just before houses and factories

  - decreases voltage

  - increases current
• Why is the voltage reduced before it reaches homes?

  Makes it safer to use because the voltage during transmission would be dangerous in homes
• Why is the P.D increased before being transmitted?

  - to reduce energy lost due to heat

  - by using a low current

  - improves efficiency of the National Grid
• Power formula


  Potential difference x current
• Power Units


  Watts (W)
• Three wires in a plug

  Live. Neutral. Earth.
• Colour of live wire

  brown
• Colour of neutral wire

  blue
• Colour of earth wire

  green and yellow
• Safety features of a plug

  - Fuse to break the circuit if too high a current flows

  - Hard plastic coating doesn't conduct electricity

  - Cable grip to prevent cable getting dislodged
• Function of live wire

  Carries 230V alternating potential difference from the supply
• Function of neutral wire


  Completes the circuit
• Function of earth wire

  Safety feature. Prevents casing of appliance becoming electrified