P3

• Cell - Transfers energy to charge

  
• Battery - two or more cells in a series circuit

  
• Switch - breaks or completes the circuit

  
• Bulb - transfers energy to surroundings as light or heat

  
• Ammeter - measures the rate of flow of charge (current)

  
• Voltmeter - measures the potential difference (volt) across a component

  
• Diode - only allows the current to flow in one direction

  
• Fuse - blows when current is too high

  
• Resistor - slows down the current

  
• Variable resistor - used to change current/resistance

  
• light dependant resistor - resistance is affected by light intensity

  
• thermistor - resistance is affected by temperature

  
• series circuit - the current is the same at every point

  
• parallel circuit - the current is shared between branches

  
• Current

  • rate of flow of charge in a circuit
  • measured in amperes using an ammeter
  • charge (C) = current (A) X time (S)
• Potential Difference

  • difference in energy between two points
  • measured in volts (V) using a voltmeter
• Resistance

  • all wires and components try to slow down the flow of charge through them
  • caused by collisions of charges with atoms as they flow through material
  • measured in Ohms (Ω)
  • higher the resistance, the lower the current
  • voltage (V) = current (I) X resistance (R)
• Energy Transfers

  • energy is transferred from store to store
  • measured in Joules (J)
  • rate of energy transfer - power
  • power (W) = energy transferred (J) / time (S)
• Power in circuits

  • rate of energy transfer (power) depends on potential difference (V) and current (A)
  • power (W) = Potential difference (V) X current (A)
• Magnetic Fields

  • all magnets have two poles (North and South)
  • magnets produce a magnetic field where another magnet will feel a force
  • magnetic fields always run north to south and are strongest at poles

  
• Earth Magnetic Field

  • compass will point to geographical north but this will be magnetic south as opposite poles attract
• Magnets

  • induced magnets are magnetic materials that can become magnetized then lose their magnetism
  • permanent magnets are always magnets
• Current and Magnetic Effect

  • current flowing through a wire induces a magnetic field around the wire
  • the magnetic field is in concentric circles
  • higher the current, the stronger the magnetic field
  • magnetic field gets weaker as you go further from current

  
• Solenoid

  • winding an induced wire into a coil produces a solenoid
  • solenoids will have the same magnetic field as a bar magnet
  • solenoids can become electromagnets if a soft iron core is placed inside coils

  
• Electromotive effect

  • an electric motor transfers electrical energy to kinetic energy
  • consists of a coil and wire sitting in a field of two opposite poles
  • magnetic field interacts causing a force to be applied to the coil
  • one side is forced up the other down, causing it to rotate
  • force (N) = magnetic field strength (T) X current (A) X length of wire (M)
• Transformers

  • change voltage of electricity depending on where it is needed
  • step up transformers have more secondary coil turns than primary
  • a voltage passes through primary coil producing a magnetic field
  • iron core is magnetised inducing a current in secondary coil
  • voltage = number of primary coil turns / number of secondary coil turns / overall voltage