electricity

• electrical current is the flow of electrical charge
• polythene rod becomes negatively charged
• acetate and Perspex become positively charged
• electric field - a region where a force acts on a charged particle
• how is a spark formed?

  normally air is an electrical insulator

  when there is a strong electric field the atoms and molecules in the air, break apart to form positive and negative ions

  the charged ions experience a force due to the electrical field

  the movement of the ions due to their attraction gives a spark
• p.d. is the energy transferred per unit charge as charges move between two points in a circuit
• 1 volt is the energy transferred when 1 coulomb of charge moves through a component
• charge is the amount of electricity that flows through a circuit in a second
• the higher the current, the higher the temperature of the filament, the hotter the bulb, the more light is emitted
• when a filament lamp gets hotter, the free electrons move faster, the metal ions in the filament vibrate more so it takes up more space

  As the metal ion take up more space, the electrons collide with then more often, the the resistance and temperature of the bulb increases
• the filament lamp is made out of tungsten as it has a high melting and boiling point and a filament lamp operates at 2000 degrees Celsius
• a thermistor can be used to turn on the heater when it get cold, act as a fire alarm, keep a fish tank from becoming too cold
• a diode is component that only allows current to flow in one direction
• the earth wire provides a low resistant path to the ground which prevents electrocution
• if the casing of a faulty appliance becomes live, the potential difference between and the earth is 230v

  if a person touches it, there is a complete circuit and the current passes through the persons body to earth. the person revives an electric shock
• the national grid is a collection of power cables and transformers that connect the power stations to factories and houses across great britain
• transformers are devices that can change the potential difference. they are made from 2 coils of wire with iron passing through them.