P1 Revision

P1 Revision

1. P1.1 The transfer of energy by heating processes and the factors that affect the rate at which that energy is transferred

   • P1.1.1 Infrared Radiation
     • All objects emit and absorb infrared radiation
     • The hotter an object is the more infrared radiation it radiates in a given time
     • Dark, matt surfaces are good absorbers and good emitters of infrared radiation
     • Light, shiny surfaces are poor absorbers and poor emitters of infrared radiation
     • Light, shiny surfaces are good reflectors of infrared radiation
   • P1.1.2 Kinetic Theory
     • The use of kinetic theory to explain the different states of matter
     • The particles of solids, liquids and gases have different amounts of energy
   • P1.1.3 Energy transfer by heating
     • The transfer of energy by conduction, convection, evaporation and condensation involves particles and how this transfer takes place
     • The factors that effect the rate of evaporation and condensation
     • The rate at which an object transfers energy by heating depends on:
       • surface area and volume
       • the material from which the object is made
       • the nature of the surface with which the object is in contact
     • The bigger the temperature difference between an object and its surroundings, the faster the rate at which energy is transferred by heating
   • P1.1.4 Heating and insulating buildings
     • U-values measure how effective a material is as an insulator
     • The lower the U-value, the better the material is as an insulator
     • Solar panels may contain water that is heated by radiation from the Sun. This water may then be used to heat buildings or provide domestic hot water
     • The specific heat capacity of a substance is the amount of energy required to change the temperature of one kilogram of the substance by one degree Celsius
       • E = m x c x 0
         • E is energy transferred in joules, J; m is mass in kilograms, kg; 0 is temperature change in degrees Celcius, C; c is specific heat capacity in J/kgC

2. P1.2 Energy and efficiency

   • P1.2.1 Energy transfers and efficiency
     • Energy can be transferred usefully, stored, or dissipated, but cannot be created or destroyed
     • When energy is transferred, only part of it may be usefully transferred; the rest is 'wasted'
     • Wasted energy is eventually transferred to the surroundings, which become warmer. The wasted energy becomes increasingly spread out and so becomes less useful
     • efficiency = useful energy/power out / total energy/power in (x100%)

3. P1.3 The usefulness of electrical appliances

   • P1.3.1 Transferring electrical energy
     • Examples of energy transfers that everyday electrical appliances are designed to bring about
     • The amount of energy an appliance transfers depends on how long the appliance is switched on and its power
     • E = P x t
       • E is energy transferred in kilowatt-hours kWh; P is power kilowatts, kW; t is time in hours, h
       • E is energy transferred in joules, J; P is power in watts, W; t is time in seconds, s
     • To calculate the cost of mains electricity given the cost kilowatt-hour

4. P1.4 Methods we use to generate electricity

   • P1.4.1 Generating electricity
     • In some power stations an energy source is used to heat water. The steam produced drives a turbine that is coupled to an electrical generator.
       • Energy sources include:
         • the fossil fuels (coal, oil and gas) which are burned to heat water and air
         • uranium and plutonium, when energy from nuclear fission is used to heat water
         • biofuels that can be burned to heat water
     • Water and wind can be used to drive turbines directly
     • Electricity can be produced directly from the Sun's radiation
     • In some volcanic areas hot water and steam rise to the surface. The steam can be tapped and used to drive turbines. This is known as geothermal energy
     • Small-scale production of electricity may be useful in some areas and for some uses, e.g. hydroelectricity in remote areas and solar cells for roadside signs
     • Using different energy resources has different effects on the environment:
       • the release of substances into the atmosphere
       • the production of waste materials
       • noise and visual pollution
       • the destruction of wildlife habitats
   • P1.4.2 The National Grid
     • Electricity is distributed from power stations to consumers along the National Grid
     • For a given power, increasing the voltage reduces the current required and this reduces the energy losses in the cables
     • The uses of step-up and step-down transformers in the National Grid

5. P1.5 The use of waves for communication and to provide evidence that the universe is expanding

   • P1.5.1 General properties of waves
     • Waves transfer energy
     • Waves may be either transverse or longitudinal
       • In a transverse wave the oscillations are perpendicular to the direction of energy transfer
       • In a longitudinal wave the oscillations are parallel to the direction of energy transfer
     • Electromagnetic waves are transverse, sound waves are longitudinal and mechanical waves may be either
     • All types of electromagnetic waves travel at the same speed through a vacuum
     • Electromagnetic waves form a continuous spectrum
     • Longitudinal waves show areas of compressions and rarefraction
     • Waves can be reflected, refracted and diffracted
     • Waves undergo a change of direction when they are refracted at an interface
     • The terms frequency, wavelength and amplitude
     • All waves obey the wave equation
       • v = f x l
         • v is speed in metres per second, m/s; f is frequency in hertz, Hz; l in wavelength in metres, m
     • Radio waves, microwaves, infra rad and visible light can be used for communication
   • P1.5.2 Reflection
     • The normal is a construction line perpendicular to the reflecting surface at the point of incidence
     • The angle of incidence is equal to the angle of reflection
     • The image produced in a plane mirror is virtual
   • P1.5.3 Sound
     • Sound waves are longitudinal waves and cause vibrations in a medium, which are detected as soun
     • The pitch of a sound is determined by its frequency and loudness by its amplitude
     • Echoes are reflections of sound
   • P1.5.4 Red-shift
     • If a wave source is moving relative to an observer there will be a change in the observed wavelength