Physics P1

Physics P1

1. HEAT

   • Particles gain kinetic energy when heated
   • measured on an absolute scale
     • unit = joule (J)
   • TEMPERATURE
     • Measure of the average kinetic energy
       • higher temp= higher KE
     • measured in degrees celcius
     • if there's a DIFFERENCE IN TEMPERATURE between two places, then ENERGY WILL FLOW between them

2. SPECIFIC HEAT CAPACITY

   • Tells you how much energy stuff can store
   • the amount of energy needed to raise the temperature of 1KG of a substance by 1 degrees celcius
     • ENERGY = MASS X SHC X TEMP CHANGE
   • water has SHC of 4200/J/Kg degrees celcius
   • SPECIFIC LATENT HEAT
     • SLH of melting = the amount of energy needed to melt 1Kg of material without changing its temperature
       • SLH of boiling= the energy needed to boil 1Kg of material without changing its temperature
     • ENERGY = MASS X SLH
     • HEATING
       • Solid
         • melting
           • liquid
             • boiling
               • gas
       • COOLING
         • gas
           • condensing
             • liquid
               • freezing
                 • solid

3. CONDUCTION

   • occurs mainly in solids
     • eg- metals
       • saucepans
   • the process where vibrating particles pass on extra kinetic energy to neighbouring particles
   • eventually extra kinetic energy is spread all the way through a solid
   • CONVECTION
     • Occurs in liquids
       • and gases
     • 1. when liquid/ gas is heated the particles move faster
       • it expands
         • becomes less dense
       • 2. warmer/ less dense fluid rises above the colder/denser surroundings
         • eg- a hot air balloon
         • 3. as warm fluid rises
           • cooler fluids take its place
           • 4. end up with a circulation of fluid
     • occurs when there more energetic particles move from the hotter region to the cooler region and take their heat energy with them
     • eg- radiators
     • HEAT RADIATION
       • How we get heat from the sun
         • radiated as infrared waves
       • different from conduction and convection
         • doesn't need a medium
         • only occurs through transparent substances
           • air
           • glass
           • water
         • amount of radiation emitted or absorbed depends on the surface colour and texture
       • all objects continually emit and absorb heat radiation
         • hotter = more emitted
           • cooler = temp increase
             • matt black = good
               • smooth/ light coloured = poor
       • important in cooking

4. SAVING ENERGY

   • Things that emit = sources
     • eg- radiators
   • things that transfer/ waste / loose = sinks
     • eg- computers
   • can insulate so the sinks drain less energy
     • costs money
       • save in the long run
   • PAYBACK TIME = INITIAL COST / ANNUAL SAVING
   • EXAMPLES
     • Loft insulation
       • fibreglass laid on floor
         • reduces convection / conduction
       • initial cost: £200 annual saving: £100 payback time: 2 years
     • hot water tank jacket
       • reduces conduction
       • initial cost: £60 annual saving: £15 payback time: 4 years
     • double glazing
       • two layers of glass with an air gap
         • reduces conduction
       • initial cost: £2400 annual saving: £80 payback time: 30 years
     • thick curtains
       • reduces convection and conduction through windows
       • initial cost: £180 annual saving: £20 payback time: 9 years
     • draught proofing
       • strips of foam/ plastic to stop hot air escaping
         • reduces convection
       • initial cost: £100 annual saving: £15 payback time: 7 years
     • cavity walls & insulation
       • two layers of bricks with a gap between them
         • reduces convection
       • initial cost: £150 annual saving: £100 payback time: 18 months
   • thermograms show when your house is leaking heat

5. EFFICIENCY

   • Machines always waste some energy
   • less energy that is wasted = more efficient device
   • EFFICIENCY = USEFUL ENERGY OUTPUT / TOTAL ENERGY INPUT ( X 100% )
   • Sankey diagrams
     • arrow thickness = amount of energy
       • wasteful = down
         • eg-

6. WAVES

   • Amplitude: from rest position to the crest
   • wavelength: crest to crest
   • frequency: number of complete cycle
   • WAVE SPEED= FREQUENCY X WAVELENGTH
   • Need to convert units for above equation
   • all waves can be reflected, refracted and diffracted
   • reflection of light lets us see things
     • light bounces off objects into our eyes
     • law of reflection =
       • ANGLE OF INCIDENCE = ANGLE OF REFLECTION
       • Incidence is towards mirror
         • reflection is away from mirror
       • total internal reflection depends on the critical angle
         • if the aoi is LESS than the critical angle -----> most light is refracted
           • EQUAL to-----> ray goes along surface
             • GREATER -----> no light comes out
   • DIFFRACTION
     • waves are spreading out
       • when they pass through a gap or pass an object
     • amount of diffraction depends on the size of the gap relative to the wavelength of the wave
       • narrower gap----> longer the wavelength----> more the wave spreads out
     • REFRACTION
       • Changing the speed of a wave can change its direction
       • waves travel at different speeds in substances which have different densities so when the wave crosses a boundary between two substances it changes speed
       • waves are only refracted if they meet a new medium at an angle. if they're travelling along the normal (i.e the angle of incidence is zero) they will change speed but are not refracted - they don't change direction

7. ELECTROMAGNETIC WAVES

   • There are seven types of Electromagnetic waves
     • occur at different wavelengths
       • shorter wavelengths = higher frequency
     • all travel at the same speed through a vacuum
   • wavelength---->
     • radio waves
       • microwaves
         • infra red
           • visible light
             • ultra violet
               • x- rays
                 • gamma rays
   • --- increasing frequency and decreasing wavelength --->
   • the properties of EM waves depend on frequency and wavelength
     • as frequency of EM radiation changes its interaction with matter changes
     • higher frequency = more dangerous
   • different sorts of signals have different advantages
     • light = great --> moves fast
       • electrical = good --> carries info quickly
         • difficult to repair optical fibres
           • wireless = good --> portable

8. communicating with light

   • can require a code
     • eg- morse code
   • can travel through optical fibres
     • carry data long distances
     • bounce waves off of the very narrow core
   • lots of advantages
     • very quick way to communicate
     • little interference
     • quick

9. LASERS

   • produce narrow, intense beams of monochromatic light
   • a special ray of visible light
     • all waves have the same frequency and wavelength
       • makes the light monochromatic
   • have low divergence - the beam is narrow and stays like that
   • CD PLAYERS
     • Surface has billions of shallow pits and lands
       • laser is shone --->CD is reflected as spun

10. INFARED

    • many uses around the home
      • remote controls to TV
      • mobile phones
      • security systems
    • used to monitor temperature
    • control electrical equipment

11. RADIO WAVES

    • Good at transferring over long distances
    • don't get absorbed by the Earths atmosphere
    • no longer than 10cm

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