Changing the way you learn

Heating Houses
1. Energy flow
  1. Energy flows from a warmer to a colder body. When energy flows away from a warm object, the temperature decreases
2. Measuring temperature
  1. A thermogram uses colour to show temperature; hottest: white/yellow coldest:black/dark blue/purple.
  2. Temperature is a measurement of hotness on a arbitary scale.
  3. When the temperature of a body increases, the average kinetic energy of the particles increases
  4. Heat is a measurement of internal energy, it is measured on an absolute scale.
3. Specific heat capacity
  1. Energy needed to raise the temperature of 1kg by 1 degree c
  2. Measured in Joules per kg degree celsius j/kgoc
  3. energy transferred = mass x specific heat capacity x temperature change
4. Specific latent heat
  1. Energy needed to melt or boil 1kg of the material
  2. Measured in Joules per kilogram J/kg
  3. energy transferred = mass x specific latent heat
  4. When a substance changes state, energy is need to break the bonds that hold the molecules together. This explains why there's no change in temperature.
Keeping homes warm
1. Practical insulation
  1. Double Glazing - Reduces energy loss by conduction. Gap between 2 pieces if filled with gas/contains a vaccum. Particles in a gas are far apart, it's very difficult to transfer energy
  2. Loft insulation - reduces energy loss by conduction and convection. - Warm air rises - Energy is transferred through ceiling by conduction - Air in loft is warmed and trapped by insulation, both sides are same temp so no energy is transferred
  3. Cavity wall- reduces energy loss by conduction and convection. Air in foam is good insulator, and the air can't move because it's caught in the foam
  4. Insulation blocks- used to build new homes, shiny foil on both sides to reduce radiation; - energy from sun is reflected to keep the home cool in summer, energy from home is reflected back to keep home warm in winter
2. Conduction, convection and radiation
  1. Conduction - due to the transfer of kinetic energy between particles
  2. Convection - Gas expands when it's heated. Less dense, so rises. Density = kg/m3
    1. Density = mass / volume
  3. Radiation doe not need a material to transfer energy. Energy can be transferred through a vaccum
3. Energy efficiency
  1. efficiency = useful energy output (x100%) / total energy input
  2. Energy from home is lost to the environment
  3. Different types of insulation cost different amounts and save different amounts of energy
  4. Payback time = cost of insulation /annual saving
  5. Buildings that are energy efficient are well insulated; little energy is lost to the surroundings
  6. Designers and architects have to make sure that little energy is lost
Spectrum of waves
1. Wave properties
  1. Amplitude - Maximum displacement of a particle from its rest position
  2. Crest - Highest point
  3. Trough - Lowest point
  4. Wavelength - distance between two successive points having same displacement
  5. Frequency - Number of complete waves passing a point in one second
  6. wave speed - frequency x wavelength
2. Getting messages across
  1. Some optical instruments such as periscope use two or more plane mirrors
  2. Refraction occurs because speed of waves decreases as wave enters a more dense medium and increases as the wave enters a less dense medium. Freq stays same but wavelength changes
  3. Diffraction is the spreading out of a wave as it passes through a gap
    1. Amount of diffraction depends on size of gap; the most diffraction occurs when the gap is a similar size to wavelengths. Effects are noticeable in telescopes and microscopes
  4. Size of communications receiver depends on wavelength of radiation
Light and lasers
1. Morse code
  1. Uses a series of dots and dashes to represent the alphabet. Used by signalling lamps as series of short and long flashes of light. Example of digital signal
2. Sending signals
  1. When sent by light, electricity, microwaves or radio, almost instantaneous
  2. Advantages and disadvantages. Can the signal be seen by others? Can the wire be cut? How far does the signal have to travel?
3. Laser light
  1. White light is made up of different colours of different freq. out of phase
  2. Has only a single frequency, is in phase and shows low divergence
  3. Used to read from the surface of a CD. As pitted, which represents digital signal, laser light is shone onto cd surface and reflection provides info for digital signal
4. Critical angle
  1. Normally refraction happens when light travels from one material to another
    1. If it's passing from a more dense material into less dense, the angle of refraction is lager than the angel of incidence
    2. When angle is 90 degrees, the angel of incidence is called the critical angle
    3. Total internal reflection - when the angle of incidence is bigger than the critical angle
    4. Some fibres are coated to improve reflection
5. Endoscopy
  1. Allows doctors to see inside a body without the need for surgery. Light passes along one set of optical fibres to illuminate inside of the body, the light is reflected and then passes up another set of fibres to the eye/camera
Cooking and communicating using waves
1. Cooking with waves
  1. Infrared radiation doesn't penetrate food easily
  2. Microwaves penetrate up to 1cm into food
  3. Microwaves can penetrate glass or plastic but are reflected by shiny metal surfaces. Special glass in a microwave open door reflects them and they can cause body tissue to burn
2. Electromagnetic spectrum
  1. Energy is transferred by waves; the amount of energy depends on the frequency or wavelength of the wave
  2. High frequency (short wavelength) waves transfer more energy
  3. Ovens cook food by infrared radiation; energy is absorbed by the surface of food, the kinetic energy of the surface increases, the rest of the food is heated by conduction
  4. Microwave ovens cook by microwave radiation- the water/fat molecules in the outer layers of food vibrate more
3. Microwaves
  1. Microwaves have wavelengths between 1mm and 30cm
  2. Phones use longer wavelengths than microwave ovens, less energy is transferred
4. Microwave radiation is used to communicate over long distances. The transmitter and receiver must be in line of sight.
  1. Satellites are used for microwave communication. Signal from Earth is received, amplified and re-transmitted back to Earth. They're in line of sight because there are no obstructions in space.
  2. Microwaves do not show much diffraction, adverse weather and large areas of water can scatter the signals, the curvature of the Earth limits the line of sight so transmitters have to be on high buildings.
  3. Mobile phones can interfere with sensitive equipment -this is why they are banned on planes and in hospitals.
Wireless signals
1. Radio refraction and interference
  1. Wireless technology is used by radio and television, laptops, mobile phones
  2. Radio waves are reflected and refracted in the Earth's atmosphere: the amount of refraction depends on the frequency of the wave/there is less refraction at higher frequencies
  3. Radio stations broadcast signals with a particular frequency
  4. The same frequency can be used by more than one radio station; the radio stations are too far away from each other to interfere/but in unusual weather conditions, the radio waves can travel further and broadcasts interfere
  5. Digital Audio Broadcasting or DAB also provides a greater choice of radio stations but the audio quality isn't as good as the FM signals. DAB eliminates interference between other radio stations
2. Radio reflection
  1. Radio waves are reflected in the ionosphere. They behave like light in an optical fibre and undergo total internal reflection
  2. Water reflects radio waves but land mass doesn't
  3. Continued reflection by the ionosphere and the oceans allows radio waves to be received from an aerial that is not in line of sight
  4. Microwaves pass through the ionosphere
  5. Microwave signals are received by orbiting satellites, amplified and retransmitted back to Earth
  6. Communication satellites orbit above the equator and take 24 hours to orbit Earth
3. Communication problems
  1. Radio waves are diffracted when they meet an obstruction
  2. Refraction in the atmosphere needs to be thought about when sending a signal to a satellite
  3. Transmitting aerial needs to send a focused beam to the satellite - aerial is small
    1. Transmitted beam is slightly divergent
  4. Some energy lost from edge because of diffraction
Stable Earth
1. Earthquake waves
  1. A seismograph shows the different types of earthquake wave
  2. L waves travel around the surface VERY slowly
  3. P waves are longitudinal pressure waves: P waves travel through the Earth between 5km/s and 8km/s
    1. Can pass through solids and liquids
  4. S waves are transverse waves. They travel through the Earth at between 3 km/s and 5.5 km/s/
    1. Can only pass through solids
2. Earth's insides
  1. P waves travel through the Earth and are refracted by the core
    1. The paths that are taken by P waves help scientists figure out how big the Earth's core is
  2. S waves are not detected on the opposite side of the Earth to an Earthquake. They can't travel through liquid, which means that it tells the scientists that the core is liquid
3. Tan or burn
  1. Tan- caused by the action of ultraviolet light on the skin
    1. Cells in the skin produce melanin, a pigment which produces a tan
      1. People with darker skin don't tan as easily because uv radiation is filtered out
  2. maximum time to spend in the sun = published normal burn time x SPF
  3. People are becoming more aware of the dangers- like sunbeds
4. Ozone depletion
  1. Scientists didn't believe that there was a thinning of the ozone layer, they thought the instruments were faulty but they compared with others and were confident in their findings
  2. Ozone is found in stratosphere
    1. Helps filter out UV radiation
  3. CFC gases (aerosols) destroy the ozone and thin it out. This increases danger to us
    1. Agreement to reduce CFC emissions
  4. The ozone layer is at its thinnest above the South Pole because the chemicals work best in cold conditions
  5. Scientists monitor the thickness by using satellities

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	Created by georgia.somerville over 10 years ago