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• for electrical charge to flow through a closed circuit there must be a source of potential difference
• current is the flow of charge
• charge = current x time
• current is measured in amps
• charge is measured in coulombs
• a current has the same value at any point in a single closed loop
• the current through a component depends on its resistance and the potential difference across it
• what does the current through a component depend on

  resistance and potential difference
• V= IR
• for some resistors the value of R stays constant but in others it changes as the current does
• the resistance of a thermistor decreases as the temperature increases
• the resistance of an LDR decreases as light intensity increases
• LDRs are used in devices that can shine light in the dark
• a thermistor is used in computer systems to activate a fan when it gets too hot
• resistance is measured in ohms
• a charged object creates an electric field around itself
• the national grid is a system of transformers and high voltage cables
• national grid connects power stations to homes
• energy is always lost in cables due to the resistance of a wire
• step up transformers increase the potential difference by several hundred thousand volts
• less energy is lost in cables when potential difference is high
• step down transformers decrease PD to 230V
• static electricity can be dangerous can cause sparks
• how to stop static electricity

  earthing the objects
• when two insulators are rubbed together electrons pass from one to the other