GCSE SCIENCE

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GCSE SCIENCE

• REVISION OF PHYSICS UNIT 1a
• Energy and Energy Resources

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PHYSICS 1a

• Key topic areas
• Heat transfer
• Using energy
• Electrical energy
• Generating electricity

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1. Heat transfer

• 1. What are the three methods of heat transfer?
• Conduction, Convection and Radiation.
• CONDUCTION
• 1. What sort of substances does conduction work
  in ?
• ALL solids, but works especially well in metals.
• 2. How does conduction work in ALL solids ?
• By VIBRATIONS being passed on from
  particle-to-particle.
• 3. Why does it work so well in metals ?
• Metals also contain FREE ELECTRONS which transfer
  the heat very rapidly.

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1. Heat transfer (cont.)

• 4. Why dont liquids conduct very well ?
• Particles too spread out to pass on vibrations
• 5. What two things will not conduct at all ?
• Gases (particles even further apart) and vacuums
  (no particles)
• 6. Can you think of any things which use the poor
  conducting ability of air to keep heat in ?
• e.g. Double glazing, woollen jumpers, quilts,
  fibre glass (used in lofts and to lag pipes)
• COMMON MISTAKE WARNING ! Fibre glass traps heat
• Wrong!
• Fibre glass traps AIR and the air DOES NOT
  CONDUCT

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1. Heat transfer (cont.)

• CONVECTION
• 1. What substances does convection work in ?
• LIQUIDS and GASES
• 2. Why not solids? Why not a vacuum?
• Particles in a solid cant move out of position.
  There arent any particles in a vacuum.
• 3. So, what are the steps in convection?
• Particles nearest the heat collide more, so move
  apart
• HOT AREA EXPANDS (-notice, NOT the particles
  expand)
• Hot area now LESS DENSE than surrounding
  fluid....
• ...so it RISES.

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1. Heat transfer (cont.)

• COMMON MISTAKE WARNING ! Heat rises
• Wrong!
• HOT PARTICLES rise
• RADIATION
• 1. How does heat radiation travel from
  place-to-place ?
• By waves infra-red waves, which can travel
  through a vacuum as they dont use particles and
  travel at the speed of light
• 2. How hot does an object have to be to emit heat
  radiation?
• Just hotter than its surroundings. e.g. An ice
  cube at 0C will emit infra-red waves if placed
  in a freezer at -4C

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1. Heat transfer (final bit!)

• 3.What sort of surfaces are best at absorbing
  infra-red waves?
• ROUGH, DULL and BLACK
• 4. What sort of surfaces are best at emitting
  infra-red waves?
• Also ROUGH, DULL and BLACK !
• It depends on the temperature of the object and
  its surroundings.
• For an object HOTTER than its surroundings, a R,
  D and B surface will get rid of the heat fastest
  ( a smooth, shiny, silver surface will keep the
  heat in longer)
• For an object COOLER than its surroundings, a R,
  D and B surface will take in heat best (a S, S, S
  surface reflects it away).

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2. Using energy

• 1. What does the Law of Conservation of Energy
  say ?
• Energy cant be created or destroyed, only
  TRANSFORMED (converted) to other forms.
• 2. Name the basic forms (types) of energy
• Nuclear
• Potential 1 Gravitational, 2 Chemical, 3
  Elastic
• Heat
• Light
• Sound
• Kinetic
• Electrical

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2. Using energy (cont.)

• You can expect some energy transformation
  questions
• e.g.1 What is the energy transformation in a
  light bulb ?
• ELECTRICAL ? HEAT LIGHT
• e.g.2 What device will carry out this
  transformation ?
• ELECTRICAL ? SOUND
• A loudspeaker
• You can expect to have to identify useful and
  waste energy in a transformation.
• useful just means the type of energy we want.
• waste energy is any form which we dont want

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2. Using energy (final part!)

• e.g. What is the useful energy and waste energy
  in this transformation in an electric motor ?
• ELECTRICAL ? KINETIC HEAT SOUND
• 100 joules ? 60J 15J
  ???
• A measure of how much energy is
  converted into useful forms in a device is called
  the EFFICIENCY of the device.
• YOU NEED TO LEARN -
• Efficiency useful energy got out total energy
  put in
• In the example above
• i) How much sound energy is released ?
• 100 (60 15) 25J
• ii) What is the efficiency of the device ?
• 60 100 0.6 (often we times by 100 to
  get efficiency, here 60)

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3. Electrical energy

• Key ideas
• Electrical devices often just asked to identify
  the energy conversion carried out or to calculate
  the effficiency (see previous)
• Electrical power need to know that the unit of
  electrical power is the WATT (W). A device which
  converts 1 joule of energy each second has a
  power of 1 watt. So ....
• 1. How much energy does a 60 W bulb convert
  in 1s ?
• 60 joules
• 2. How much energy does a 1 kW heater
  convert in 1s?
• 1 kW 1000 W, so it will convert 1000
  joules each s.

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3. Electrical energy (cont.)

• Electricity bills
• You need to be able to use the two formulae-
• energy in kWh power in kW x time in h
• cost in p number of units x
  price per unit
• IMPORTANT! energy in kWh and number of
  units are THE SAME THING. So you can drop your
  answer from the first formula into the second
  formula.
• e.g. How much does it cost to run a 3kW heater
  for 5h if electricity costs 6p per unit ?
• 1st formula energy in kWh 3 x 5 15kWh (or
  15units)
• 2nd formula cost in p 15 x 6 90p

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3. Electrical energy (final part!)

• The National Grid know the stages-
• IN POWER STATION
• 1. turbine turned by steam, water, wind
• 2. generator makes the electricity
• THE NATIONAL GRID
• 3. step-up transformer raises voltage (and
  reduces
• current) at power station before
  transmission
• 4. power lines (or transmission lines)
• 5. step-down transformer lowers voltage
  (and raises
• current) for customer

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4. Generating electricity

• You should know that we generate electricity from
  two forms of resources
• Non-renewable name some ?
• Nuclear, Fossil fuels (coal, oil, gas)
• Renewable
• Solar, Wind, Wave, Hydro, Biomass,
  Geothermal, Tidal
• KNOW THE ADVANTAGES AND DISADVANTAGES OF EACH
  !!!!!!

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4. Generating electricity (cont.)

• NON-RENEWABLE
• All can be used to generate large amounts of
  electricity RELIABLY
• You get the same amount of energy from 1kg of
  nuclear fuel as from 1000kg of coal
• ...but all are running out and...
• ...all have environmental problems
• - nuclear waste dangerously radioactive for 1000s
  of years.
• - coal when burnt releases CO2 (adds to global
  warming, acid rain) and SO2 (acid rain)
• oil when burnt releases CO2 ,SO2 and NOx (acid
  gases)
• natural gas (methane) when burnt releases CO2
• BUT ....NONE OF THESE DAMAGE THE OZONE LAYER!

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4. Generating electricity (final part!)

• RENEWABLE
• All are renewable so the energy in them is
  constantly being replaced and wont run out.
• Hard to capture the energy in some (e.g. solar)
  and some not very reliable (e.g. wind)
• Need to know
• How we can capture the energy in each one
• What are the good points about each one
• What are the bad points about each one.
• YOU NEED TO BE ABLE TO WEIGH UP THE GOOD BAD
  POINTS OF DIFFERENT ONES AND CHOOSE

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THE END !

• GOOD LUCK IN YOUR EXAMS