electricity

• Electrical system

  Comprises of electrical components, connecting wires, electric cell, circuit board, light bulb
• Electric circuits

  • Made up of electrical components
  • All components must be connected correctly for it to work
  • A circuit diagram shows how the components are connected
• Flow of electricity in an electric circuit

  1. Electric current flows through a path set up by an electric circuit

  2. Incomplete circuits are called open circuits

  3. Electrical components must be joined together without any gap to form a closed circuit
• Flow of electricity in an electric circuit

  Similar to flow of water molecules in a water model
• Switch

  Used to open or close a circuit
• Types of switches

  • Main switch used in buildings
  • Switches used on circuit boards
• Resistor

  • Electrical component that is specially made to have a certain resistance
  • Can be connected in a circuit to resist the current flow
• Types of resistors

  • Fixed resistors
  • Variable resistors
• Fixed resistor

  Has only one resistance value
• Variable resistor

  Can be adjusted to change the resistance
• Types of variable resistors

  • Rotating rheostat
  • Sliding rheostat
• Resistance

  Affects the brightness of a light bulb

  
• Ammeter

  Instrument used to measure electric current

  
• Voltmeter

  Instrument used to measure voltage or potential difference

  
• How to connect ammeter

  Always connected in series in a circuit
• How to connect voltmeter

  Must be connected in parallel to a circuit or electrical component
• Potential difference (p.d.)

  Measure of the amount of electrical energy converted to other forms of energy when per unit of electric charge flows through the component
• Resistance

  Electrical component that hinders the flow of electric charges when connected in a circuit
• Short circuit

  Electrical circuit that allows a current to travel along an unintended path, often where zero (or a very low) electrical resistance is encountered
• Adding a resistor in series

  Increases the total resistance in the circuit, decreasing the current flowing through the light bulb and making it dimmer
• Adding a resistor in parallel

  Decreases the total resistance in the circuit, increasing the current flowing through the light bulb and making it brighter
• Effects of electric current

  • Chemical
  • Lighting
  • Heating
  • Magnetic
• Electromagnet

  Magnet made by making current flow in a wire coiled around a metal rod (e.g. iron)
• Electromagnet

  • The coil of wire is called a solenoid
  • Solenoid generates an electromagnetic field, disrupting the Earth's magnetic field and deflecting a compass needle
• Solenoid

  Coil of wire that generates an electromagnetic field
• Increasing magnetic effect of an electromagnet

  Can be done by increasing current, increasing number of turns of wire, or winding the coil around an iron rod
• Uses of electromagnets

  • Crane that lift iron/steel
  • Electric bell
  • Magnetic levitation train
  • Electric motor
  • Magnetic resonance imaging (MRI)
• Telephone

  Uses a changing magnetic effect to cause a thin sheet of metal (diaphragm) to vibrate
• Electromagnet

  A temporary magnet which can be turned on and off using electric current
• How to increase magnetic effect

  1. Increasing the current in the wire coil (increasing number of batteries)

  2. Increasing the number of turns of wire in the coil

  3. Winding the coil around an iron rod
• Uses of electromagnet

  • Crane that lift iron/steel
  • Electric bell
  • Magnetic levitation train
  • Electric motor
  • Magnetic resonance imaging (MRI)
• Telephone receiver and mouthpiece

  • At the mouthpiece, a varying electric current is generated
  • Current flows through the circuit
  • Magnetic effect of varying current causes electromagnet to alternately attract and repel the iron diaphragm
  • Sound wave is produced
• Electric bell

  Electromagnet and magnet interact to cause the bell to ring
• Magnet

  A permanent magnet retains magnetism until it is purposely demagnetised (spoilt)
• In an electric motor, both permanent magnets and electromagnets are found
• Our homes have many circuits hidden behind walls that are intricately connected and have to be in good working condition to function perfectly
• A short circuit can cause extensive damage
• Electrical Hazards

  • Electric shocks and electrocution
  • Electrical fires
• Electrocution

  Occurs when a person is injured or killed by a large current passing through the body
• Short circuit

  Occurs when the live wire touches the neutral wire, providing a shorter path of low resistance for the current to flow through