Physics P1 Revision

Physics P1 Revision

1. Energy

   • Heat
     • Can be transferred by conduction, convection, or radiation
     • Infrared radiation
       • Electromagnetic waves
       • Dark matt surfaces absorb and emit information best
       • Shiny silver surfaces best reflect heat
     • All objects absorb and emit radiation
     • Rate of heat transfer depends on surface area
     • Specific heat capacity
       • Energy (E in Joules)= Mass (M in kg) x Specific Heat Capacity (J/kgC) x Temperature change (theta)
   • Types of energy
     • Electrical Light Sound Kinetic Nuclear Thermal Gravitational Elastic Chemical
       • The last three are forms of stored energy
   • Conduction, Convection and Radiation
     • Conduction
       • Kinetic theory explains the 3 states of matter (solid, liquid, gas)
         • Solid- strong forces of attraction, not much energy so can only vibrate around fixed positions
         • Liquid- weaker forces of attraction, mcan form irregular arrangements, more energy so can move in random directions at low speeds
         • Gases-No attraction between the particles, and the most energy, and are free to move at high speeds
       • Mainly in solids.
       • Extra kinetic energy turns into heat
       • Best in metals because of free electrons
     • Convection
       • Liquids and gases only
       • Circle of heating, travelling then cooling
     • Heat radiation infrared energy
       • Bigger surface area, more infrared waves can be emmitted
   • Energy Transfer
     • Condensation and evaporation
       • When a gas cools and lose kinetic energy
       • If it gets close enough the gas becomes a liquid
       • Vice versa for evaporation
       • The rate of evaporation is best due to high temperatures, low density, larger surface area, and high airflow

2. Electricity

   • Cost of Electricity
     • Energy= Power x time
     • kWh=Kilowatt-hours
     • Total energy from two metre readings= subtract the smaller from the end
   • Electrical Appliances
     • Which one is more cost effective or uses less energy
     • Standard of living is affected by access to electricity
   • Energy and the Environment
     • Renewable energy
       • Wind power- turbines create no pollution, very noisy, rely on wind, high initial cost but no running costs and no permanent damage
       • Solar Cells- No pollution, but some to create them, very reliable during the day in sunny countries, high initial costs, Expensive to connect to the national grid
       • Hydroelectric is is used in dams and falling water- expensive and difficult to build, reliable, cheap to connect to the national grid, loss of habitats
       • Pumped storage is used to save energy
       • Geothermal and biofuel use heat
     • Non renewable energy
       • Creates CO2 through combustion, sulphur dioxide causing acid rain, nuclear waste is dangerous
     • Comparisons
       • Initial costs, reliability issues, environmental issues, set up/decommissioning time, running costs, location issues
   • National Grid
     • Current creates heat so a step up/step down increases voltage to decrease current and vice versa
     • How electricity is transferred

3. Waves

   • Basics
     • Waves have amplitude- height from the middle, wavelength, which is from crest to crest, or frequency in Hz
     • Transverse waves have sideways vibrations
     • Longitudinal waves are along the same lines
     • Wave Speed (m/s)= Frequency (Hz) x Wavelength (m)
   • Refraction + Diffraction
     • Diffraction - waves spreading out.
       • When a gap is the same size as wavelength= maximum diffraction
     • Refraction- changing speed changes direction
       • Crossing a boundary between 2 substances EG glass to air
   • Electromagnetic Spectrum
     • Radiowaves Microwaves Infrared Visible Light X-ray Gamma Rays
       • Radiowaves are used for communication
       • Microwaves are used for satellite communication and mobile phone
       • Infrared used for remotecontrols

4. Origin of the universe

   • Red shift
     • Light is shifted towards the red end of the spectrum
     • Shows that everything is moving away from us
   • Big Bang
     • Cosmic background microwave radiation was origionally gamma rays when the big bang occurred
       • This has been stretching out since the Big bang proving that the universe is expanding

5. Efficiency

   • In the home
     • Short payback time
     • Cavity wall insulation- stops convection and radiation
     • Loft insulation stops conduction and radiation
     • Draught proofing- Reduce convection
     • Hot water tank jacket-reduces conduction and radiation
     • Thick curtains- Conduction and radiation
   • Efficiency= Useful Energy Out/ Total energy in
   • Useful energy is concentrated energy
   • The entire energy output of a machine end up as heat
   • Sankey Diagram- Always to scale