Physics P1

• Radioactive decay is the random process where nucleus gives out radiation as it changes so it becomes more stable.
• Alpha

  • absorbed by the skin and sheet of paper
  • helium atom with 2 protons and neutrons
  • most ionising
  • least dangerous from a distance
• Beta

  • absorbed by aluminium
  • ejected from the nucleus as neutrons turn to protons
  • less ionising than alpha
  • most dangerous at a mid range.
• Gamma

  • Most penetrating (most dangerous at a distance)
  • least ionising
  • can be stopped by thick lead or concrete.
  • electrom radiation from the nucleus.
• Half-life is the time taken for number of nuclei in and isotope to halve.
• charge flow = current x time
• If resistance increases, current decreases.
• Direct current - passes through in the same direction. Current of cells and batteries.
• Alternating current - changes direction of current in the National Grid.
• • Earth wire ( yellow and green) there for safety, stops appliance from becoming live.
  • Live wire ( brown ) 230V - carries alternating potential difference from power supply.
  • Neutral wire ( blue ) completes the circuit.
• • Step up transformer - increases potential difference from the power station to transmission cables. This reduces current and thermal energy making it more efficient.
• • Step down transformer - decreases the potential difference to increase safety.
• Thermistor - at a low temp, there’s high resistance. at a higher temperature resistance decreases.
• LDR - at a low light, resistance is high. At high light intensity, resistance decreases.