KS4 Using Electricity

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Year 10 Using Electricity
Learning Objectives

Students should understand the following:

  • When certain insulating materials are rubbed against each other they become electrically charged. Negatively charged electrons are rubbed off one material and on to the other. The material that gains electrons becomes negatively charged. The material that loses electrons is left with an equal positive charge.
  • When two electrically charged objects are brought close together they exert a force on each other. Two objects that carry the same type of charge repel. Two objects that carry different types of charge attract. Attraction and repulsion between two charged objects are examples of non-contact force.
  • Students should be able to:
    - describe the production of static electricity, and sparking, by rubbing surfaces
    - describe evidence that charged objects exert forces of attraction or repulsion on one another when not in contact
    - explain how the transfer of electrons between objects can explain the phenomena of static electricity.
  • A charged object creates an electric field around itself. The electric field is strongest close to the charged object. The further away from the charged object, the weaker the field.
  • A second charged object placed in the field experiences a force. The force gets stronger as the distance between the objects decreases.
  • Students should be able to:
    - draw the electric field pattern for an isolated charged sphere
    - explain the concept of an electric field
    - explain how the concept of an electric field helps to explain the noncontact force between charged objects as well as other electrostatic phenomena such as sparking.
  • Mains electricity is an ac supply. In the United Kingdom the domestic electricity supply has a frequency of 50 Hz and is about 230 V.
  • Students should be able to explain the difference between direct and alternating potential difference.
  • Most electrical appliances are connected to the mains using three-core cable.
  • The insulation covering each wire is colour coded for easy identification:
    - live wire – brown
    - neutral wire – blue
    - earth wire – green and yellow stripes.
  • The live wire carries the alternating potential difference from the supply.
  • The neutral wire completes the circuit. The earth wire is a safety wire to stop the appliance becoming live.
  • The potential difference between the live wire and earth (0 V) is about 230 V.
  • The neutral wire is at, or close to, earth potential (0 V).
  • The earth wire is at 0 V, it only carries a current if there is a fault.
  • Students should be able to explain:
    - that a live wire may be dangerous even when a switch in the mains circuit is open
    - the dangers of providing any connection between the live wire and earth.
  • Students should be able to explain how the power transfer in any circuit device is related to the potential difference across it and the current through it, and to the energy changes over time.
  • Power = potential difference × current (P = V I)
  • Power = current2  x resistance (P = I2 R )
  • Everyday electrical appliances are designed to bring about energy transfers.
  • The amount of energy an appliance transfers depends on how long the appliance is switched on for and the power of the appliance.
  • Students should be able to describe how different domestic appliances transfer energy from batteries or ac mains to the kinetic energy of electric motors or the energy of heating devices.
  • Work is done when charge flows in a circuit.
  • The amount of energy transferred by electrical work can be calculated using the equation: energy transferred = power× time (E = P t)
  • energy transferred = charge flow × potential difference (E = Q V)
  • Students should be able to explain how the power of a circuit device is related to:
    - the potential difference across it and the current through it
    - the energy transferred over a given time.
  • Students should be able to describe, with examples, the relationship between the power ratings for domestic electrical appliances and the changes in stored energy when they are in use.

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