electricity

• build up of static is caused by friction
• when certain insulating materials rub against each other, negative electrons will be scraped of one and put onto another
• electrons will go from the cloth to the polyethene rod
• only electrons move in static electricity, the loss of electrons causes a positive charge
• As electric charge builds up, the voltage between the object and the earth increases. If the voltage gets large enough, electrons can jump across to the earth and cause a spark.
• voltage is the force which drives the flow of electrons and is provided by the cell
• resistance is everything which opposes the flow of electrons and is measured in ohms
• when resistance stays constant, when voltage increases, current increases proportionally
• filament lamp

  
• a diode

  
• resistor, the negative part is when the battery is attached the opposite way

  
• diodes only allow a current to flow in one direction they create a very high resistance in the opposite direction
• charge is the measure of total current that flowed within a certain period of time and is measured in coulombs
• in series circuits voltage is shared across all compnments. VT=V1+V2+V3
• in series circuits, current is the same throughout and is measured with an ammeter which can be placed anywhere
• in series circuits, the total resistance is equal to the individual resistance of each component
• in series circuits, a voltmeter must be placed parallel at the component
• in parallel circuits there is usually only one component on each loop. each component will get full voltage (the same as the total voltage)
• in parallel circuits, the current is shared but doesnt have to be equal across all components
• in parallel circuits, loops with greater resistance will have a lower current and more components equals a lower total resistance
• open switch

  
• closed switch

  
• filament lamp

  
• fuse that breaks if there is too much current (saftey)

  
• diode which only allows current to flow in one direction

  
• LED (light emitting diode) emits light when current flows in one direction

  
• ammeter measures current and must be placed in series

  
• voltmeter measures voltage and must be placed in parallel

  
• resistor restricts the flow of electrons

  
• variable resistor allows the resistance to be modified

  
• LDR (light depending resistor) makes the resistance dependent on the light intensity, the higher the light intensity, the lower the resistance making the current higher

  
• thermistor makes the resistance dependent on temperature, the higher the temperature, the lower the resistance making the current higher

  
• PowerStations on the national grid generate thermal energy and convert it into electrical energy
• a high current produces lots of thermal energy due to resistance which wastes lots of energy
• step up transformers lower the current and increase the voltage to reduce wasted energy
• step up transformers have more coils on the secondary coil
• step down transformers then lower the voltage back down to 230v for houses
• high voltage is dangerous and can blow appliances up
• alternating current flows in both directions due to an alternating potential difference
• all mains supply is alternating current and is 230v and 50 Hz