Physics GCSE OCR Gateway P1 - Energy For The Home

Physics GCSE OCR Gateway P1 - Energy For The Home

1. Heat and Temperature

   • Heat
     • Measure of kinetic energy
     • Absolute scale
       • Can't go below 0
       • Joules (J)
   • Temperature
     • Measure of hotness
     • Not absolute scale
       • Celcius
       • Farenheit
       • Kelvin
       • Can go below 0
   • Specific Heat Capacity (c)
     • How much energy a material can store
     • Energy = Mass x Specific Heat Capacity x Temperature Change
       • E = m x c x △t
     • J/kg/°C
     • Water has c of 4200 J/kg/°C

2. Melting and boiling

   • Energy is needed to break intermolecular bonds
   • Flat spots on heating graphs = melting/boiling/condensing/freezing point
   • Specific Latent Heat
     • Energy needed to change state
     • J/kg
     • Energy = Mass x Specific Latent Heat
       • E = m x slh

3. Conduction, Convection + Radiation

   • Conduction
     • Occurs mainly in solids
     • Vibrating particles hit other particles
       • Kinetic energy passed on to neighboring particles
   • Convection
     • Occurs mainly in liquids and gases
     • Particles heat up, move faster, become less dense
       • Heated particles rise, cooler ones take its place + heat up
         • Convection currents form
   • Radiation
     • Infrared
     • Needs no medium to travel through
       • Can travel through vacuums e.g. Space
     • Can only occur through transparent substances
     • Amount of radiation emitted/absorbed depends on colour and texture
       • Matt Black surfaces absorb and emit well
         • Reflect poorly however
       • Shiny surfaces absorb and emit poorly
         • Reflect well however

4. Saving Energy

   • Home insulation methods
     • Loft insulation
       • Fibreglass 'wool' laid across loft floor
       • Reduces conduction from ceiling to roof space
     • Hot water tank jacket
       • Reduces conduction
     • Double glazing
       • Two layers of glass with air gap between
       • Reduces conduction
     • Thick curtains
       • Reduces conduction and radiation through window
     • Draught-proofing
       • Foam and plastic strips around doors and windows
       • Reduces convectinon
     • Cavity walls and Insulation
       • Two layers of bricks with air gap between
         • Insulating foam in air gap
       • Reduces conduction and convection
   • Efficiency
     • The less energy wasted, the more efficient a device is
     • Efficiency (%) = Useful Energy Output / Total Energy Input x 100

5. Waves

   • Have Amplitude, Wavelength and Frequency
     • Amplitude - Displacement from rest position
     • Wavelength - Length of one full cycle
     • Frequency - Number of cycles per second
   • Wave speed = Frequency x Wavelength
   • Properties
     • Can be reflected, refracted or diffracted
       • Reflection of light is why we can see things
         • Angle of incidence = Angle of relfection
       • Diffraction - Waves spread out when passing through a gap or pass an object
         • Maximum diffraction when gap is same width as wavelength
       • Refraction - Change in wave speed, which can cause a change in direction
         • Waves travel slower in denser mediums
           • If wave enters denser medium at an angle, part of wave slows down before another part, causing it to change direction
   • EM Waves
     • Radio
     • Micro
     • Infra-red
     • Visible Light
     • Ultra-Violet
     • X-Ray
     • Gamma Ray
     • Properties depend on frequency and wavelength
       • Higher frequency = more dangerous to living cells
       • Waves at end of spectrum pass through stuff
       • Waves in middle of spectrum get absorbed by stuff