Electrical systems

• Electrical circuit


  The path along which the electric current moves
• Electrical components


  • Connecting wires
  • Bulb
  • Switch
• Closed circuit


  Electrical components are joined together without any gap in between to form a closed circuit
• Open circuit


  Incomplete circuit, electricity cannot flow
• Sources of electrical energy

  • Batteries (electric cells)
  • Electrical mains socket from power station
• Cell/Battery


  Portable sources of electricity that convert chemical potential energy to electrical energy
• All cells have a positive (+) terminal and a negative (-) terminal
• Electric current


  The rate of flow of electric charges, measured in amperes (A)
• Electron flow


  Actual motion of electrons when current is flowing, from negative to positive terminal
• Conventional current


  An idea agreed upon by scientists, from positive to negative terminal
• The direction of conventional current is opposite to the direction of electron flow
• Potential difference

  The amount of work done to drive a unit charge through a component, measured in volts
• Electrical resistance, 


  A measure of how much a component opposes the flow of electric current, measured in ohms
• Conductors


  • Have low resistance, allow current to flow
  • Examples: Copper, Silver
• Insulators


  • Have very high resistance, do not allow current to flow
  • Examples: Plastics, Rubber
• Resistors


  • Electrical devices that control the flow of current by controlling resistance
• Types of resistors


  • Fixed resistors
  • Variable resistors
• Fixed resistor


  Resistor of known value that cannot be changed
• Variable resistor


  Resistor that can vary resistance in a circuit, commonly known as a rheostat
• Series circuit


  • Has only one path in which the charge can flow
• Parallel circuit


  • Has more than one path in which the charge can flow
• Series circuit


  Resistance increases, current decreases
• Circuit


  Path through which the charge can flow
• Types of circuits


  • Series
  • Parallel
• Circuit diagram


  Visual representation of a circuit
• Resistance increases


  Current decreases
• Resistance decreases


  Current increases
• Variable resistor


  Device used to change the resistance in a circuit
• How a variable resistor works

  1. Current flows in

  2. Slider is moved to adjust length of wire current flows through

  3. Current flows out
• Slider moved to the right

  Resistance increases
• Slider moved to the left

  Resistance decreases
• Electricity can be converted into many forms of energy
• Electric heating


  Conversion of electrical energy to thermal energy
• Heating elements


  • Made of nichrome which has high resistance and can withstand high temperatures
  • Heat up rapidly when electric current passes through
• Filament lamp


  Converts electrical energy to light energy
• Filament


  • Tungsten wire with small cross-sectional area and coiled
  • Heated to 2500°C when electric current flows through, generating light
  • Tungsten used due to high resistivity and high melting point
• Damaged insulation on wires can expose conducting wires and cause electric shocks
• Overheated cables can lead to electrical fires, caused by overloaded power sockets or use of inappropriate wires
• Water in contact with exposed electrical wires provides a conducting path for current, leading to electric shocks
• Circuit breakers


  Safety devices that can switch off electrical supply when large currents flow through them