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Heating Houses

Temperature is a measurement of hotness on an arbitrary scale

Heat is a measurement of internal energy on an absolute scale

Specific Heat Capacity: the energy needed to raise temperature of 1kg by 1degree C, measured in Joules per kilogram

Specific Latent Heat: the energy needed to boil/melt 1Kg of the material, measured in Joules per kilogram 

When a substance changes state, energy is needed to break the bonds that hold the molecules together, this is why there is no change in temperature 

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Keeping homes warm

Conduction:the transfer of kinetic energy between particles 
Convection:A gas expands when heated, this makes it less dense so it rises
Radiation:Electromagnetic spectrum, can transfer energy through a vaccum
Double Glazing:The gap between the 2 pieces of gas is filled with gas or contains a vaccum, particles in a gas are very far apart=hard to transer energy, hard to transfer energy through conduction
Loft Insulation: reduces energy loss through conduction+convection, warm air in the home rises, energy is transferred through the celing by conduction, air in the loft is warmed by the top of the cieling and then trapped by the loft insulation, both sides of the ceiling are the same tempearture so no energy is transferred 
Cavity Wall Insulation:The air in the foam is a good insulator , the air cannot move by convection becasue it's trapped in the blocks 
Insulation blocks used to build homes have shiny foil on both sides to reduce enrgy transfer by radiation, in the summer the radiation is reflected back to keep the house cool, in the winter, heat from the home is reflected back to keep the home warm
Payback time=cost of insualtion
                       annual savings                       

 

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A Spectrum of Waves

Amplitude: Maximum displacement of a particle from it's rest position 
Wavelength: Distance between to successive points on a wave having the same displacement and moving in the same direction
Frequency: Number of complete waves passing a point in 1 second

Electromagnetic Spectrum:

increasing WL<---  radio--microwave--infared--visible--ultraviolet--x ray--gamma  --->increasing freq

Refraction occurs because the speed of a wave decreases as the wave enters a more dense medium and increases as the wave enters a less dense medium 

Diffraction:
The spreading out of waves as it passes through a gap
The most diffraction occurs when the gap is the same size to the wavelength
Big gaps shows less diffraction  

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Light and Lasers

Morse code is an example of a digital signal 
White light is made up of different colours of different frequencies out of phase 
Lasers:A single frequency, in phase and shows low divergence  
Laser light is used to read information off a CD:

  • The surface of the CD is pits
  • The pits represent the digital signals
  •  Laser light is shone on to the CD surface and the difference in reflection provides the information for the the digital signal 

Critical Angle:
If the light is travelling from a more dense material into a less dense, the angle of refraction is larger than the angle of incidence
When the angle of refraction is 90 degrees, the angle of incedence is called the critical angle
If the angle of incedence is bigger than the critical angle, the light is reflected=total internal reflection
Endoscopy is used to see inside the body without the need for surgery, it uses total internal reflection  

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Cooking and Communicating with Waves

Cooking: 
Microwaves:Penetrate up to 1cm in food! Water//fat molecules vibrate more, kinetic energy increases, energy is transferred through food by conduction
Microwave Properties: Reflected by metal or shiny surfaces,wavelength-1mm to 30cm 
Infared:Energy is absorbed by the surface of the food,the kinetic energy increases, rest of the food is heated by conduction.  
Electromagnetic energy:High frequency waves transfer more energy
Mircowave Communication: 
Microwaves radiation is used to communicate over long distances,the transmitter and reciever must be in line of sight 
Satellites are used, the signal from earth is transmitted, amplified and re-transmitted back
Signal Strength:
Adverse weather can scatter microwave signals
The curvature of the earth can effect signals so satellites have to be on tall buildings and close together
Microwaves do not show much diffraction  

 

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Data Transmission

Digital Signals on a TV remote:
Pressing a button on the remote completes a circuit, a coded signal is sent to the LED at the front of the remote, the LED transmitts a series of pulses, this is recieved by the device and decoded to allow the television to change channels etc. 
The switchover from analogue to digital as many perks:  

  • Improved signal quality
  • A greater choice of programmes 
  • Can interact with programmes 
  • Information services 

Analogue Signals: Were added to a carrier wave, the frequency of the carrier wave was usually higher, interference can be added to the carrier wave and transmitted,if the wave is amplified so is the interference 

Advantages of digital signals: 
Multiplexing which allows many signals to be transmitted at once
Interference is not apparent becasue the digital signals only have two values 

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Wireless Signals

Radio waves are refracted and reflected by the earths atmosphere, there is less refraction at higher frequencies
Radio stations have to broadcast at different frequencies unless the stations are too far apart to interfere however unusual weather conditions can cause signals to travel further
Interference is reduced if digital signals are used
DAB(digital audio broadcasting) vs. FM
DAB has a greater choice of stations however the audio quality isnt as good, DAB eliminates interference
Radiowaves are reflected from the ionsphere-they undergo total internal reflection
Water reflects radio but land mass does not, this allows radio waves to recieved from an aerial not in line of sight
Microwaves pass through the ionsphere
Communication Problems:
Radio waves are diffracted when they meet an obstruction,
Refraction in the atmosphere needs to be taken into account when sending a signal to a satellite
The transmitted beam is slightly divergent
Some enrgy is lost from the edge of the transmitting aerial due diffraction

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Stable Earth

A seismograph shows the different types of earthquake waves 
L waves: travel round the earths surface very slowly
P waves: Longitudinal pressure waves, travel at 5km/s to 8km/s, can travel through solids and liquids-They are refracted by the core, the path taken by the p waves means we can work out the size of the earth's core
S waves: Transverse waves, travel at 3km/s to 5km/s, can ONLY travel through solids,
They are not detected on the opposite side of the earth to an earthquake,this tells us the earths core is liquid
Tan or burn: Cells in the skin produce melanin, a pigment that produces tan, people with darker skin do not tan becasue the UV is filtered out
Max length of time to spend in sun=normal burn time x SPF
Dangers of UV: Skin cancer, premature skin aging, cataracts, sun burn 
Ozone Depletion
Ozone layer is found in the stratosphere and filters out UV radiation
CFC's from fridges and aerosols destroy the ozone layer
The ozone layer is thinest at the poles because the CFC's work best in cold conditions
There is an international agreement to reduce CFC's  

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