quizlet

• Diode


  very high resistance (no current) until a specific voltage

  
• Live wire


  Carries current to an appliance at a high voltage
• Neutral wire


  completes circuit and has same current as live wire but low / zero voltage
• Earth wire


  for protection and prevents shocks or electrocution if live wire touches the metal casing of an appliance
• How does an MCB work

  trips if current is too large

  electromagnet pulls a switch, breaks circuit

  easy to reset

  stops fires, protects appliances
• How does an RCCD work

  -trips when imbalance in current between the live and neutral wires

  -switch is opened breaking the circuit
• Advantages of RCCD


  -very sensitive

  -very fast to react

  -protects people
• Fossil fuel burning power station

  -Fossil fuel is burned to heat water. -Steam turns a turbine which is connected to a generator which produces electricity as it rotates.

  -electricity is supplied to the national grid.

  -steam is cooled and sent back to the furnace to be heated again
• Step up transformer


  -Increases the voltage which decreases the current.

  -Lower current through cables means less energy loss as

  heat.

  -Increases the grid's efficiency
• Step down transformer


  -reduces voltage before it is supplied to consumers.

  -Lower voltages are safer.
• Series circuit


  -Equal current everywhere in the circuit

  
  

  -Voltage is shared between the components,

  -Voltage adds up to the total component voltage
• Parallel circuit


  -Current is shared between the components

  -but must add to the current from the power source

  -Equal voltage across each component
• Filament lamp


  Resistance increases at higher voltages

  
• Resistor or wire (at a constant temperature)

  Constant resistance

  
• Calculating density of an irregularly shaped solid

  1. Measure the mass (weight)

  2. Fill a measuring cylinder with water to a specific volume

  3. Place the solid in the measuring cylinder and record the new volume

  4. Calculate the volume of the solid by subtracting the initial volume (step 2) from the new volume (step 3)

  5. Calculate the density using density=mass/volume
• Calculating density of a liquid

  1. Measure the mass of an empty measuring cylinder

  2. Fill the measuring cylinder with a specific volume of the liquid

  3. Measure the combined mass of the measuring cylinder and the liquid

  4. Calculate the mass of the liquid by subtracting the empty mass (step 2) from the new mass (step 3)

  5. Calculate the density using - density=mass/volume
• Conduction


  -Heat energy causes the particles to vibrate more and is then transferred from one particle to the next as they collide.

  -Happens in solids
• Why are metals the best conductors

  Because they have free electrons that can move the energy quickly from the hot side to the cold
• Why is air a good insulator

  Because the particles are very far apart, reducing the rate of collisions and making it more difficult for the heat to transfer from one side to the other.
• Convection


  -Heat energy causes the particles to gain kinetic energy (move quicker) and make them farther apart.

  -This means it will be less dense.

  -This less dense liquid or gas will rise above the denser cold liquid, forming a convection current.
• Radiation


  -All warm things emit heat radiation in the form of infrared waves.

  -Hotter bodies emit more radiation than cold bodies.
• Loft insulation


  -Reduces conduction. -Fibreglass wool between the ceiling and the loft space has pockets of trapped air which acts as an insulator

  
• Double glazed windows


  -Reduces conduction. -Trapping air between two layers of glass acts as an insulator

  
• Stopping draughts


  -Reduces convection.

  -Stops cold air being sucked into the house as the hot air inside rises.
• Floor insulation


  -Reduces conduction.

  -Fibreglass wool below the floor has pockets of trapped air that acts as an insulator.
• Cavity walls


  -Reduces conduction.

  -Trapping air between two layers of bricks acts as an insulator.

  
  

  -Filling the cavity (gap) with fibreglass wool or foam stops the air in the gap moving and reduces convection
• Payback time equation


  Payback time = installation cost /annual saving
• Alternating current


  Continuously changes direction and size

  
• Direct current


  -Voltage and current have a constant size and direction

  -Supplied by batteries

  
• Advantages of a ring main circuit

  - Current can travel two ways so you can make the wires thinner and have a lower current in each part

  - You can add more sockets anywhere on the ring and each will have the same voltage

  
• How does a fuse work

  -Stops the current if it becomes too large by melting a wire in the fuse.

  -fuse must be replaced once it has 'blown'

  - prevents the device overheating
• Transverse wave


  -Vibrations are perpendicular (90 degrees) to the direction of travel of the waves e.g. electromagnetic waves

  
• Longitudinal wave


  -Vibrations are parallel to the direction of travel of the wave e.g. sound waves

  
• Wavelength


  Length of one complete wave (m)

  
• Amplitude


  Maximum displacement (height of a wave)

  
• What is the bottom of a wave called

  Trough
• What is the top of a wave called

  Peak
• Frequency of waves in deep and shallow water

  Equal
• Wavelength of waves in deep and shallow water

  Longer in deep
• Wave speed of waves in deep and shallow water

  Bigger in deep