OCR P1

OCR P1

HEATING HOUSES
1. energy is a form of heat
  1. flows from a warmer body to a cold body
  2. when energy flows away from a warm object to the temperature of the object decreases
2. thermogram is used to show temperature through colours
  1. hottest: white and yellow and coldest: black,purple,blue
  2. temperature is measured in hotness
    1. on an arbitrary scale
    2. thermogram used to compare temperatures o objects
    3. the temperature of the body increases so does the kinetic energy
    4. SHC -specific heat capacity
      1. energy needed to raise the temperature of 1kg to 1.c
        measured in j/kg.c
      2. when an object is heated and its teperature increases and energy is transferred
        energy transferred= mass * SHC* temperature change
        SLH
        specific latent heat
        energy needed to boil/melt 1kg of material it is measured in j/kg
        this differs for different materials
        when an object is heated it changes state, energy is transferred but temperature remains constant
        this is because the substance is needed tochange state the energy is needed tyo break the bonds that hold the molecules together this explains why the temperature doesnt change
        energy transferred= mass * SLH
practical insulation
1. double glazing
  1. loft insulation
    1. cavity wall insulation
      1. insulation blocks
        reduces energy by radiation
      2. reduces energy loss by conduction and convection
    2. reduces energy loss by conduction and convection
  2. reduce energy loss by conduction
2. conduction,convection,radiation
  1. conduction
    1. transfers kinetic energy from one particle to another
      1. mainly happens in solids
  2. convection
    1. is when less dense particles rise and more dense particles fall
      1. happens in gasses and liquids
  3. radiation
    1. does not need a material to transfer energy through vacuum
sanky diagrams are used to measure energy efficiency
1. in the sanky diagram some energy is wasted due to the surroundings
  1. building that are energy efficient are well insulated this means less energy is lost by surroundings
wave properties
1. amplitude is the maximum displacement of a particle from a rest position
  1. crest of the wave is the highest point on a wave above the rest position
    1. the trough of a wave is the lowest point on the wave below its rest position
      1. the wavelength of a wave is the distance between two successive points on a wave
        the frequency of a wave is the number of complete wave passing through one point
2. radio
  1. microwave
    1. infrared
      1. visible
        ultraviolet
        x-ray
        gamma ray
        increasing frequency
  2. increasing wavelength
3. refraction occurs when the speed of waves decrease as the wave enters a more dense medium and increases as the wave enters a less dense medium, the frequency stays the dame but wavelength changes
  1. diffraction the spreading out of a wave as it passes a gap
    1. differation depends on the size off the gap. more diffraction occurs when the gap is the similar size to the wavelength but less diffraction occurs when the gap is large
      1. seen through telescopes and microscopes
lights and lazers
1. Morse code is a digital code which consists of . and -
2. sending signals through light, microwaves, electricity or radio
  1. laser light- has a single frequency in one phase and shows low divergence
    1. laser light used to read cd's it does it as it reads the digital signals by different reflection
3. critical angle
  1. when the angle of refraction is 90' the angle of incidence is the same as the critical angle.
    1. when the angle of incidence is bigger than the critical angle it is total internal reflection
      1. telephone conversations and computer data are transmitted long distance along optical fibres at the speed of light.
        fibres are coated to improve reflection
        endoscopes are used to see inside a body without the need for surgery
cooking with waves
1. infrared radition is used to cook food but can not penetrate easily through food
2. microwaves can penetrate through 1 cm of food
  1. microwaves can penetrate glass or plastic but is reflected by shiny mental surfaces
    1. but it can burn human tissue
electromagnetic spectrum
1. energy is transferred by waves
  1. amount of energy depends on the frequency or the wavelength of the waves
    1. high frequency has a short wavelength this means the wave is transferring more energy
    2. normal ovens cook food using infrared radiation the energy is absorbed by the food and the kinetic energy of the surface of the food particles increase.
      1. the rest of the food is heated up using conduction
    3. microwave oven cook food using microwave radiation the fat and water molecules in the outer layer of the food vibrates more
      1. it too uses conduction to heat the rest of the food
        microwaves have a wavelength between 1mm and 30cm
        mobile phone use longer wavelengths than microwave ovens as less energy is transferred by mobile phones
        microwaves in communication - microwaves are used in communication over long distance
        the transmitter must be in the line of sight with the receiver
        aerials are normally situated aat the top of high buildings
        satellites are used for microwave communication
        the signal from earth is received, amplified and re transmitted back to earth
        large aerials can handle thousands of phone calls and tv channels at once
        signal strength from mobile phones can change a lot over a short distance
        microwave do not show diffraction
        adverse weather and large areas of water can scatter the signals
        curvature of the earth limits the line of sight so transmitters have to be on tall buildings or close together
        mobile phones can interfere with sensitive equipment that is why they are banned on airplane and hospitals
        scientists publish their studies to allow others to check there findings
digital signal
1. infrared signals carry information that allow electronic and electrical devices
  1. the light emitted diode -LED is sent when pressing the remote
    1. digital signal is better than analogue signals as improves the signal quality also a greater choice of programmes, being able to interact with programmes and also has subtitle and guides
optical fibre
1. allow data to be transmitted very quickly using pulses of light

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	Created by Maaria Talha about 9 years ago