Electricity

• Why is a live wire dangerous even when something is switched off?

  The live wire is at 230V. Any connection between the live and earth wires will increase the current. This causes the wires to melt and catch on fire. If a person is a part of the connection, they will be electrocuted
• Explain trampoline hair in detail

  1. When a child bounces on a trampoline, the electrons are transferred between the child and the trampoline due to friction
  2. If the child gains electrons, they become negatively charged; if they lose electrons, they become positively charged
  3. Each hair has the same charge as the others, and the child's head
  4. There is a non-contact electrostatic force of repulsion between the child and the hairs
  5. This causes the hair to separate
• What happens in an electric field?

  Charged objects in an electric field experience an electrostatic force
• How do resistance and current link to each other?

  The greater the resistance of the component, the smaller the current for a given potential difference
• The current through an ohmic conductor (at a constant temperature) is...

  directly proportional to the potential difference across the resistor. This means that the resistance remains constant as the current changes
• What does the filament lamp represent?

  The resistance of a filament lamp increases as the temperature of the filament lamp increases (the graph looks like a f )
• What does the diode represent?

  The current, through a diode, flows in only one direction. The diode has a very high resistance in the reverse direction. (the graph is flat and then grows)
• The resistance of a thermistor decreases as...

  the temperature increases
• The resistance of an LDR decreases as ....

  light intensity increases
• For components connected in series:

  • There is the same current through each component
  • The total potential difference is shared between components
  • The resistance of two components is the sum of the resistance of each component
• For components connected in parallel:

  • The potential difference across each component is the same
  • The total current through the whole circuit is the sum of the currents through the separate components
  • The total resistance of two resistors is less then the resistance of the smallest individual resistor
• What is the frequency in UK mains?

  50 Hz
• What is the voltage in UK mains?

  230 V
• What is an example of direct curent?

  A cell
• What type of current if the UK mains?

  Alternating
• What is alternating current?

  The current is constantly changing direction
• What is the benefit of AC?

  it is very easy to use in a transformer to increase or decrease pd
• What is direct current?

  When the current flows in one direction
• What is the brown wire?

  Live wire
• What is the blue wire?

  Neutral wire
• What is the green and yellow stripes wire?

  Earth wire
• What type of current is in the live wire?

  Alternating current
• What is the function of the neutral wire?

  Completes the circuit
• What is the function of the earth wire?

  Safety wire to stop the appliance becoming live
• What is the potential difference between the live and earth wire?

  about 230 V
• What is the voltage in the earth wire?

  0 V, it only carries a current if these is a fault
• What does the amount of energy an appliance transfers depend on?

  how long the appliance is switched on and the power output
• What is the national grid?

  A system of cables and transformers linking power stations to consumers
• What are step up transformers used for?

  • increase potential difference
  • decrease current
• What are step-down transformers used for?

  • decrease potential difference
  • increase current
• What happens when insulating materials are rubbed against eachother?

  They become electrically charged
• What happens if a material gains an electron?

  Becomes negatively charged
• What happens if a material loses an electron?

  Becomes positively charged