P1 Revision

P1 Revision

1. temperature is a measure of how hot something is

   • measured in degrees celcius
     • can also be measured in kelvin and sometimes degrees fahrenheit
   • it can be represented by a range of colours on a thermogram
     • hottest areas appear white/yellow/red
     • coldest areas appear black/dark blue/purple
   • heat is a measurement of energy and is measured in joules
     • air is a good insulator because the particles are far apart.
       • heat energy doesn't stay in one place it moves around, hot air rises and is relaced by colder air
   • the temperature of an object is a measurement of the average kinetic energy of the particles in the object
   • if there is a difference in temperature between an object and its surroundings then heat energy flows from the hotter region to the cooler
     • if an objects temperature rises it is taking in heat energy
       • room temperature is known as ambient temperature
     • if an objects temperature falls it is giving out heat energy
     • the hotter something is the quicker it will cool
       • the rate depends on the difference between the temperature of the object and the ambient temperature around it, the greater the difference the greater the rate

2. the amount of energy needed to raise the temperature of an object depends on

   • the mass of the object
   • the change in temp required
   • the material it's made from
   • total energy supplied = energy supplied per second x number of seconds

3. each material has a value of how much energy it can hold, this is also known as specific heat capacity (SHC)

   • SHC is the energy needed to raise the temperature of 1kg of material by 1 degree
   • energy = mass x specific heat capacity x temperature change

4. energy is needed to melt or boil substances

   • when a material is changing state its temperature will stay the same
   • during the melting and boiling of water the energy supplied is used to break intermolecular bonds as the water molecules begin to change state

5. the amount of energy required to melt or boil 1kg of material is called the specific latent heat, it depends on

   • the material
   • the state
   • energy = mass x specific latent heat specific latent heat = energy / mass

6. saving energy in the home

   • materials that allow energy to flow through them quickly are called conductors
     • material that allow energy to flow through them much slower are called insulators
   • design features in the house can help save energy by reducing heat loss by conduction, convection and radiation
     • an important consideration with each method is pay back time
       • payback time = cost of installing insulation / annual saving
     • a cavity wall is made up of an inner and outer wall serarated by cavity (space) filled with air
       • the heat energy passes through the wall by conduction. this heats the air in the cavity. the heat is then carried away from the wall by convection.
         • the cavity can be filled with foam so that heat loss by conduction is reduced

7. energy efficiency is a measure of how good an appliance is at converting input energy into useful output energy.

   • efficiency = (useful output energy / total input energy) x 100

8. conduction is the transfer of heat energy through a substance from a hotter region to a cooler region without any movement of the substance itself

   • as a substance is heated the kinetic energy of the particles increases, this kinetic energy is transferred between the particles and along the substance
     • metals have free electrons which can move through a metal carrying energy

9. convection is the transfer of heat energy from hotter regions to cooler regions by the movement of particles

   • as a liquid or gas gets hotter its particles move faster causing it to expand and become less dense. the particles in the hotter region will rise up and be replaced by cooler less dense particles

10. hot objects emit infra red radiation (an electromagnetic wave) which can pass through a vacuum

    • the amount of radiation given out or taken in by an object depends on its surface
      • dark matt surfaces emit more radiation than light shiny surfaces at the same temperature

11. light is a transverse wave, a transverse wave has the following features

    • amplitude - the maximum disturbance caused by the wave
    • wavelength - the distance between corresponding points on 2 successive disturbances
    • freqency - the number of waves produced in one second

12. the electromsgnetic spectrem

    • you can calculate the speed of a wave by
      • wave speed = frequency x wavelength
        • all electromagnetic waves travel at the same speed in a vacuum
    • rabbits mate in very unusual xpensive gardens

13. reflection, refraction and diffraction

    • light or another electromagnetic wave can be reflected from mutiple surfaces
    • a wave will speed up or slow down as it passes from one material into another. this can cause the wave to change direction this is known as refraction
      • light and infrared rays can be reflected and refracted when they cross a glass-air boundary. it depends on the angle of incidence
    • as waves pass through a gap or an opening the edges spread out, this is diffraction
      • maximum diffraction occurs when the gap is the same width as the wavelength of the wave passing through it
    • optical fibres are used to send infomation in the form of pulses of light or infrared radiation.
      • an optial fibre is a long, transparent, flexible cable of very small diameter
      • optical fibres allow the rapid transmission of data necessary for modern day communications
        • pules of light or infrared are totally internally reflected

14. electromagnetic radiation can be used to send infomation without optical fibres because it can be reflected and refracted in the same way as visible light

    • wireless technology is used in radios, mobile phones and laptops it has 3 main advantages
      • signals are available 24 hours a day
      • no wiring is needed
      • items can be portable and convenient

15. morse code was used to communicate over long distances this code uses long and short flashes of light to represent letters

    • light used for communication is produced by a laser. a laser produces a narrow intense beam of light
      • produces a narrow beam of monochromatic (single colour) light
        • are used by dentists and doctors
        • produce a beam of light in which light waves all have the same frequency, are in phase with eachother and hove low divergence
          • in phase means that all the peaks and troughts go up and down toghether
            • they transfer alot of energy
    • optical fibres are used to carry signals in binary code
    • signals
      • light
        • travles very fast & small loss of signal
          • can't be used for wireless signalling as it doesn't diffract well
      • electrical
        • can be sent along wires
          • signal deteriorates
      • radio waves
        • can be used for wireless signalling as the waves can diffract around obstacles
          • diffraction leads to signal loss

16. electromagnetic radiations have many uses

    • the amount of radiation that is absorbed or emitted from a surface depends on:
      • surface temperature, colour and texture
    • microwaves are used to heat materials as well as for satellites they:
      • are absorbed by water a fat molecules which cause them to heat up increasing the kinetic energy of the particles, energy is then transferred to the center of the food by conduction or convection
      • can pentrete about 1cm of food
      • can cause burns when absorbed by body tissue
      • can travel through glass and plastics
      • are reflected by shiny metal surfaces
      • microwaves are used to transmit infomation over large distances that are in line of sight
        • the microwave signals that phones use aren't the same wavelenght as the microwaves used in microwave ovens
          • there are some concerns about microwaves emmited having dangerous effects like tumors, brain damage and chnages to DNA
            • if they are harmful children will be more at risk because there skulls are thinner
            • mobile phones masts are also belived to be harmful however there isnt enough evidence suporting this and scintists publish conflicting evidence
        • microwave signals can be lost or effected by:
          • large obstacles such as trees which block the signal, microwaves aren't diffracted around large objects
          • poor weather and large areas of surface water
          • the curvature of the earth
          • interferance between signals
          • these problems can be reduced by
            • limiting the distance between transmitters
            • positioning masts in high places like hills
    • infrared red rays are used to heat materials in cooking they are:
      • used to heat the surface of food (absorbed) increasing the kinetic energy of the particles energy is then transferred to the center of the food by conduction or convection
      • reflected off shiny surfaces
      • absorbed by black objects
      • it is a type of electromagnetic wave
        • can be used for many devices such as:
          • remotes
            • each button on a remote has a different code when the button is pressed the code is transmitted to the tv as a series of flashes
              • analogue signals can be used to transmit data they continuously vary in amplitude
                • they can have any value within a fixed range of values
                • both digital and anologue suffer with interferance in the form of noise, but interferance doesn't affect digital signals because the signal is still only on or off, the information is in the pulse pattern
              • digital signals can be used to transmit data as a series of pulses
                • they don't vary, they only have 2 states on and off (there are no values inbetween)
                • 2 or more digital signals can be sent down an optical fibre at the same time this enables more infomation to be sent at a time
                • new DAB (digital audio broadcasting) radios recive digital signals
                  • most are able to recive old FM radio station signals which are transmitted by anouluge signals
                  • advantages are more stations are available, and there is less interferance
                  • disadvanges are audio quality isnt as good as FM, some areas can't recive it because the radio waves can't diffract round the hills
          • sensors
          • short distance wireless data links for phones and computers
          • burglar alarms
          • security lights
    • microwaves and infrared energy are transferred to materials in diferent ways

17. radiation used for communication can be reflected by the atmosphere. radio stations and other nearby broadcasters must transmit using different frequences to avoid interferance

    • wireless communication is used in tvs, radios and mobiles
      • advantages - no connection to a phone land line required, portable and convinent allows access everywhere
      • disadvantages - ariel is needed to pick up the signal
    • sateliltes can be used for global communication
      • a signal is sent from a ground station transmitter dish to a satelilte reciever dish, a return signal is then sent back to earth
        • the ionosphere is an electrically charged layer in the earths upper atmosphere
          • longer wavelengths radio waves are reflected by it, this enables readio and tv programmes to be transmitted between differnet places
          • diffraction and refraction can affect communication
            • refraction results in the waves changing direction
            • diffraction changes the direction and intensity of the waves also it cause the wave to spread out the transmission dishes so signal is lost

18. eartquakes cause shock waves that travel through the earth

    • this can cause tsunamis
      • these waves are called seismic waves and can be detected by seisometers
        • there are 2 types of seismic waves - p waves and s waves
          • p-waves (primary waves) are longitudinal and travel througn solids and liquids
          • s-waves (secondary waves) are tramsverse and only travel through solids and are alot slower
            • after an earthquake occurs seismic waves are detected all over the world
              • p waves are detected in most places because they can travel through the solid crust and mantle and liquid core
                • s-waves are only detected closer to the earthquake (epicentre) so an travel through the solid mantle and crust but not the liquid core
                  • many scientists belive that we are suffering global warming 3 factors that conrtibute to this are:
                    • increasing energy in homes and industrys
                    • increased carbon dioxide emmisions from fossil fuels
                    • deforestation
                    • weather patterns can be affected as well
                      • dust from volcanoes reflects radiation causion cooling
                        • the sun produces electromagnetic waves including ultra violet radiation prolonged exposer can cause health problems
                          • if you wear factor 20 sunscreen it means you can stay in the sun for 2o x longer than usual if you keep applying it
                          • ozone gas is found natrually high up in the earths atmosphere and it prevents too many harmful ultraviolet rays reaching the earth
                            • recently scientists have noticed the link between the decreasing cases on skin cancer and the thinkness of the oszone layer
                            • to get accurate data you must repeat your experiment, use other scientists data and test your predictions
                            • the impact of the discovery of the hole in the ozone layer above antartica had an impact gloabally
                              • legislations have now been passed and CFS's are banned

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