Temperatures are represented on a thermogram:
Hot areas: white/yellow/red Cold areas: Black/dark blue/purple
Temperature is a measurement of hotness on an arbitrary or chosen scale.
Temperature is a measurement of the average kinetic energy of particles.
Equation for energy/specific heat capacity:
energy = mass x specific heat capacity x temperature change
Heat is a measurement of energy on an absolute scale.
Specific latent heat:
energy = mass x specific latent heat
Even though energy is still being transferred, there is no temperature change when materials are boiling, melting or freezing.
This is because during the melting and boiling of water, the energy supplied is used to break intermolecular bonds as the water molecules change state.
Kinetic energy of the particles increase as substance is heated. This kinetc energy is transferred between the particles and energy is transferred along the substance.Metals have free electrons which can move through the material carrying energy.
As a liquid 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 particles from the colder, denser region.
An electromagnetic wave (infrared) and requires no medium.
Saving Energy in the Home
Reduces convection and conduction by trapping layers of air between fibres.
Reduces conduction and convection by trapping air between the panes of glass.
Cavity Wall Insulation:
Reduces convection and conduction by trapping air in the foam.
In a cavity wall there is air inbetween the inner and outer wall. This means that conduction is reduced (air is a good insulator) but convection can still take place. Foam is added so conduction is reduced (air in the foam) and also convection is reduced, the air cannot move/is trapped.
Saving Energy in the Home 2
Payback time = initial cost/annual saving
Convection, Conduction and Radiation in the home:
- Kettles made of metal have shiny surfaces to reduce heat loss by radiation.
- Hot water tanks are made of stainless steel and may also have a shiny outer layer to reduce heat loss by radition. They also sometimes have an insulating jacket to reduce heat loss by conduction and convection.
Main features of a transverse wave:
- trough and crest
wave speed = frequency x wavelength
Refraction occurs because a wave will change speeds as it passes through the mediums. This causes the wave to change direction.
As a waves passes through a gap or opening, the edges spread out.
Maximum = same width as the wave.
This phenomenon limits the resolution and quality of the image produced by telescopes and optical microscopes. As light passes beween two neighbouring particles, it is diffractied. The intensity of the image is reduced. The light may also interfere with other diffracted light waves, distorting the image further.
Reindeer Meat Is a Very Unusal Xmas Gift
Radio, Microwaves, Infrared, Visible Light, Ultraviolet, Xray, Gamma
Radio = longest wavelength/lowest frequency
Gamma = shortest wavelength/highest frequency
Light and Lasers
Light is used in communication:
- signals sent in the form of Morse code which is a series of on off signals
- signals relayed between stations to cover larger distances
Morse code is a digital signal because the light is either on or off.
Advantages and disadvantages:
Light - fast, small loss of signal but can't be used for wireless (doesnt diffract)
Electrical - sent along wires but signal deteriorates.
Radio Waves - wireless (can diffract around obstacles) but diffraction leads to signal loss.
Light and Lasers 2
What happens to light when it hits a boundry - below, at and above the critical boundry:
Below - refracted away from the normal.
Above - total internally reflected and not refracted.
At - light travels along the boundary.
To be totally internally reflected, the light rays must hit above the critical angle.
Total internal reflection happens in optical fibres. Optical fibres are used for rapid transmission of data necessary for modern-day communications.
Light and Lasers 3
Lasers produce a narrow beam of light of a single colour (monochromatic).
Lasers produce an intense coherent beam of light because:
- waves have the same frequency
- waves are in phase with eachother
- waves have low divergence
Laser beams are used in CD players by reflection from the shiny surface:
- information stored on the bottom surface of the CD
- information is stored digitally
- information in the form of patterns of bumps (known as pits)
- a CD will contain billions of pits
- when the CD spins, laser light is reflected by the pits
- the reflected pluses of light are turned into electrical signals on their way to the amplifier.
Properties of infrared radiation:
- heats the surface of the food
- reflected by shiny surfaces.
Properties of microwaves:
- penetrate around 1cm into food
- reflected by shiny surfaces
- can cause burns when absorbed by body tissue
- pass through glass and plastics
Microwaves are absorbed by water and fat molecules in the outside layers of the food, increasing kinetic energy of the partcles. Energy is transferred to centre of food by conduction or convection.
Infrared is absorbed by all particles on the surface of the foood, increasing kinetic energy of the particles. Energy is then transferred to the centre of the food by conduction or convection.
The amount of energy a microwave or an infrared waves has depends on its frequency, and this determines how potientially dangerous it could be.
Microwaves can be lost or affected by:
- Large obstacles. Microwaves are not diffracted around large obstacles.
- Poor weather conditions and large areas of surface water, scatter signals.
- The curvature of the earth.
- Interference between signals.
Problems of signal loss are reduced by:
- limiting distance between transmitters
- high positioning of transmitters
Dangers of Microwaves
Microwaves could cause ear or brain tumours, brain damage or changes to DNA.
The use of mobile phones could cause the above due to the microwaves emitted from them. The risk is increased if the phones are used more frequently.
This could also be argued if you live next to a mobile phone transmission mast due to the possible dangers of microwaves.
Scientists publish studies into the effects of microwave radiation from mobile phone transmission masts. This enables other scientists to share their studies and check data from other scientists.
Sometimes their is conflicting evidience about studies such as mobile phone safety. Society must make their own choices by balancing risk and benefit about their own mobile phone use and/or to live next to a mast.
The infrared signal from a TV remote control uses digital codes to control the different functions of the TV. Each function has a different code. When a button is pressed the code is transmitted to the TV as a series of flashes (digital signals).
It is easier to remove noise from digital signals because the signals are either on or off. This means that interference is easily removed.
(Multiplexing and optical fibres)
Two or more digital signals can be sent down the same optical fibre at the same time. This enables more information to be sent in one go.
Radiation used for Communication
Radiation used for communication can be refracted and reflected, this can be an advantage and disadvantage for good signal reception.
Common uses of wireless technology:
- TV and radio
- mobile phones
Long distance communication depends on:
- the refraction and resulting relection of waves from the ionosphere
- being recieved by and re-transmitted from satellites.
The refraction and reflection in the ionosphere is similar to the TIR of light.
Nearby radio stations use different transmission frequencies to reduce interference.
Advantages and disadvantages of DAB radio:
A - more stations available and less interference with other broadcasts
D - may give poorer audio quality to FM and not all areas are covered.
Refraction and diffraction of radiation can affect communications:
- refraction at the interfaces of different layers of the earths atmosphere can result in the waves changing direction
- diffraction by transmission dishes results in signal loss because the waves spread out.
Longitudinal P waves: travel through both solids and liquids and travel faster than S waves.
Transverse S waves: travel through solids but not liquids and travel slower than P waves.
Help provide structure of the earth:
- P waves travel through solid and liquid rock (ie. all layers of the Earth), solid crust, mantle, outer core and inner core.
- S waves cannot travel through liquid rock, only detected near the epicentre of an earthquake. They can only pass through the crust and mantle.
Darker skins (more melanin) reduce skin cancer risk:
- absorb more ultraviolet radiation
- less ultraviolet radiation reaches underlying body tissues.
Factor 30 SPF = 20 mins x 30 = 600 minutes
Public health campaigns have informed people about the risks of ultraviolet rays. They use a range of media in the campaigns: TV adverts, leaflets, newspapers, internet campaigns.
The ozone layer protects the earth from UV radiation because it prevents too many harmful UV rays reaching the earth by reflecting them back into space.
- environmental pollution has depleted the ozone layer
- this allows more ultraviolet radiation to reach the earth
- the potiential danger to human health increases because of this
Scientists have varified their measurements of ozone reduction and increased confidence in their explanation by:
- measurements repeated with new equipment
- measurements repeated by different scientists
- predictions tested based on the explanation
Discovery of the hole in the ozone layer over Antarctica changed the behaviour of society at an international level:
- legislation was passed in many countries to ban the use of CFCs in fridge cooling fridge systems
- old fridges and freezers containing CFCs must be disposed of according to strict guidlines
- CFCs are no longer used as propellants in aerosol cans (hairspray and deodrant)