Electricity

• What is a current?

  Current is the rate of flow of electric charge.
• What is the unit for current?

  Amps, A
• How does a current flow?

  current flows from the positive to the negative terminal of a cell.
• What instrument is used to measure current?

  An Ammeter
• Why are metals used to make wires?

  They are used to make wires because they are good conductors of electric current because they have delocalised electrons.
• How do you calculate electric charge?

  charge = current x time
• What is voltage?


  Voltage is the amount of energy transferred to each coulomb of charge that passes.
• What happens to electrons when they pass through a cell?

  They gain energy.
• What happens to electrons when they pass through a circuit?

  They lose energy.
• What is the unit for voltage?

  Volts, V.
• 1 Volt is equivalent to?

  1 J/C
• what is the equation that links energy transferred, charge and voltage?

  Energy transferred = charge x voltage
• What is resistance?


  Resistance is the opposition of a component to the flow of electric current through it.
• What is the unit for resistance?

  ohms
• What does resistance control?

  It controls the size of the current in a circuit.
• Components with high resistance allow a low or high current to flow?

  Low current
• Components with low resistance allow a low or high current to flow?


  high.
• Why are wires often made of copper?

  Copper has a low resistance.
• What is the formula that links voltage current and resistance?

  Voltage = Current x resistance
• What is power?

  The rate at which energy is transferred.
• What is the formula that links power, current and voltage?

  power = current x voltage

  P = IV
• What is the unit for power?

  Watts, W or J/s
• How does a fuse work?

  - If the current flowing through the wire becomes too high, the fuse will heat up and melt

  - This will break the circuit
• How do you select a fuse size?

  The fuse should always have a current rating that is slightly higher than the current needed by the appliance.
• What is the equation that links energy transferred, current, voltage and time?

  energy transferred = current x voltage x time

  E = IVt
• When is work done in a circuit?

  Work is done when a current flows through the circuit.
• What are some examples of electrical safety hazards?

  overheating of wires

  damaged insulation
• What are some safety devices designed to protect users?

  - Fuses

  - Double insulation

  - Earthing

  - Circuit breaker
• What is an electrical insulator?

  A material that does not allow electric current to flow through it easily.
• What is an electrical conductor?

  A material that allows electric current to flow through it easily.
• give uses of static electricity.

  • photocopiers
  • inkjet printers
  • electrostatic spray painting
  • electrostatic precipitators
• What are some dangers of static electricity that are linked to an airplane?

  • when an airplane is in the air, friction between the airplane and air can cause the airplane to become charged
  • when the airplane lands this charge can escape to the earth as a spark
  • if the airplane is being refuelled this charge can cause an explosion
• How can we reduce the risks of sparks when refuelling an airplane?

  • attach an earth wire to the airplane to allow the charge to flow into the earth
• Explain how static electricity is used in a photocopier.

  • Inside the image drum, the ink is positively charged
  • the drum is then lasered with the text/image that is being copied
  • this text/image has a negative charge
  • so the positively charged ink will be attracted to the negatively charged drum
  • drum is pressed/rolled against a paper that is more negatively charged
  • positively charged ink will be attracted to the drum and paper and will stick on the paper
• Explain how static electricity is used in electrostatic painting.

  • ink droplets in the spray gun have the same charge
  • object being painted will have the opposite charge
  • so the ink droplets will repel one another forming a thin layer that spreads evenly on the object
• Explain how static electricity is used in electrostatic precipitators.

  • pollutant particles pass through a negatively charged mesh
  • pollutant particles become negatively charged
  • pollutant particles move higher up the chimney and are attracted to the positively charged metal plates
  • pollutant particles re trapped on the metal plate while cleaner smoke leaves the chimney