Heat is a meausure of energy and is measured on an absolute scale
There is no such thing as cold energy, if something is cold it means it lacks heat energy
Temperature is a meature of hotness, the hotter something is in comparison with its surroundings, the quicker it will cool down
A thermogram indicates temperature
Heat energy always flows from hotter too cooler bodies
Specific Heat Capacity is the energy needed to raise the temperature of a 1kg block of material. A high specific heat capacity means that the material will take a lot of energy to heat up and has to lose a lot to cool down
Specific Latent Heat is the energy needed to change the state of 1kg of a material. A high specific latent heat means it takes a lot of energy to change its state
The particles in a hot object have more kinetic energy than a cold object
Heat is transferred by conduction by the particles vibrating and making those next to them vibrate
Conduction only occurs in solids as the particles cannot move around
Warm air is less dense so rises
Convection is the movement of air from one place to another
Heat is transferred by radation as a wave
Radiation can occur in all states of matter and a vacuum as it doesnt need particles
Trapped air is a good insulator as the particles arent close enough together for conduction to take place and the particles cant move so convection cant take place
Some cavity walls have foam in the gap, this is called cavity wall insulation
Electromagnetic waves travel in straight lines
The EM spectrum in order of wavelength is:
Gamma > Xray > Ultraviolet > Infared > Microwave > Radiowave
If wavelength increases the frequency decreases
Reflection is when a wave changes direction by bouncing off a surface
Refraction is when a wave changes direction by entering a different material
refraction occurs because waves go at different peeds in different materials
Diffraction is when waves spread out after going through a gap/opening
Diffraction occurs the most when the gap is a similar size to the wavelength
Using light increases the speed of communication
Total internal reflection is when a wave stays inside a material by bouncing off the internal walls, this occurs when the angle of incidence is equal to or bigger than the critical angle for the materials
If the angle of incidence is too small the light will leave the material rather than staying inside.
Lasers produce an intense narrow beam of light of a single colour
The waves in a laser beam are coherent, which means they are all in phase.
Lasers can be used in surgery and dental treatment, for cutting materials in industry, weapon guidance and in laser light shows.
Morse code is a series of on off signals, which means it is digital.
The best enitters and absorbers are dull and black.
The worst emitters and absorbers (and so best reflectors) are shiny and white. Mobile phones use microwave signals
Properties of infrared radiation include: heats the surface of the food and is reflected by shiny surfaces.
Infrared is absorbed only by particles on the surface of the food increasing their energy.
This energy is then transferred to the rest of the food by conduction and convection.
Properties of microwave radiation include : they penetrate (about 1 cm) into food, are reflected by shiny metal surfaces , can cause burns when absorbed by body tissue and can pass through glass and plastics.
Water and fat absorb microwaves.
Microwaves are absorbed only by water and fat in the outer layers of the food increasing their kinetic energy.
When microwaves transmit information there is some signal loss due to interference, the curvature of the earth, no diffraction around objects and adverse weather.
The evidence of dangers from mobiles is not conclusive, therefore it is not easy to decide on the siting of phone masts.
As you increase the frequancy of a microwave the energy increases.
Analogue signals have a continuously variable value.
Digital signals are either on (10 or off (0). Everyday uses of infrared radiation include : remote controls and short distant data links.
Infrared sensors detect body heat.
Advantages of digital signals include: that it is easier to remove noise and you can use multiplexing.
Multiplexing is when you send more than one signal on a carrier wave.
The advantages of using optical fibers include: multiplexing and lack of interference in the final signal.
Wireless technology uses electromagnetic radiation.
The advantages of wireless technology are :no exernal/direct connection to a telephone needed , portable and convenient, allows acces when on the move.
The advantages of DAB radios are : more stations avaliable , less interference with other broadcasts.
The disadvantages of DAB radios are : poorer quality compared to FM , not all areas covered.
Radiation used for communication is refaced ansd reflected andthis can be an addvantage or disadvantage for good reception
Common uses of wireless technology include : TV and radio, mobil phones and laptop computars.
Radio waves (like light) exhibit total internal reflection.
Shock waves from earthquakes can be detected by seismometers and recorded on a seismograph.
Shock waves from earthquakes can cause damage to buildings and the earth's surface and tsunamis.
P waves are longitudinal and travel through both solid and liquid.S waves are transverse. S waves only travel through solids. P waves travel faster than S waves.
Exposure to UV radiation can cause: suntan, sunburn; skin cancer, cataracts and premature skin aging.
Sunscreens can reduce damage to skin. SPF stands for sun protection factor.
Darker skins have lower risk of cancer as they absorb more ultraviolet radiation so less UV reaches the underlying tissues.
The ozone layer protects the earth from ultra violet radiation.
Scientists were suprised to find the ozone hole.
The ozone layer has been depeted by environmental pollution from CFC's