GCSE Science - P5

GCSE Science - P5

1. Current

   • The flow of negative electrons around a circuit
   • Cannot flow through an insulator because electrons are not free to move
   • In a current metal conductors are full of charges which are free to move
   • Depends on the Voltage and Resistance
     • Voltage is measured in volts (V) and is the driving force that that pushed the current around a circuit
     • Resistance is measure in ohms (Ω) and is caused by components in the circuit (e.g. lamps). It slows down the current.
   • Measured in Amps
   • Power is the rate at which an electrical powers supply transfers energy to an appliance
     • Measured in Watts (W)

2. Circuit Components

   • Light Dependant Resistors (LDR) changes its resistance depending on how much light there is
     • Brightness - resistance falls Darkness - resistance rises
   • A Voltmeter measures the potential difference (voltage). They are always set in parallel
   • A Thermistors resistance changes with the temperature. Hot - resistance drops Cold - resistance rises
     • Hot - resistance drops Cold - resistance rises
   • A Filament Lamp lights up when resistance is created by electrons colliding with metal ions in the metal coil (or filament)

3. Transformers

   • Used to "step up" or "step down" the voltage using electromagnetic induction
     • Electromagnetic Induction is when movement plus magnetism create a current. As the magnet turns, the magnetic field through the coil changes inducing a voltage.
   • Works by;
     • Changing voltage across primary coil
       • Which changes the current in the primary coil
         • Which changes the magnetic field
           • Which changes the voltage across the secondary coil
             • Which changes the current in the secondary coil
   • Works only on AC Voltages (alternating current)

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