- Created by: Andrea Dart
- Created on: 06-01-10 15:47
Temperature - a measure of how hot something is, units degrees Celcius.
Heat - a measurement of energy, units Joules.
A difference in temperature between 2 objects results in the flow of heat energy from the hotter region to the cooler region.
Measuring heat energy;
Total energy supplied = Energy supplied /second X Number of seconds.
Specific Heat Capacity;
The energy needed to raise the temperature of 1kg of material by 1 degree Celcius.
Each material has it's own value, which is a measure of how much energy it can hold.
Energy (J) = Mass(kg) X SHC (J/kg 0C) X Temperature change (0C)
Melting and Boiling
Water cannot get a higher temperature than 100 0C, that is because at that temperature all the energy is used to change state to gas.
When ice melts any heat energy supplied is used to change it's state from solid to liquid.
Specific Latent Heat;
The amount of energy required to melt or boil 1kg of a material is called the specific latent heat. It depends on;
- the material
- the state (solid, liquid or gas)
Energy (J) = Mass (kg) X Specific Latent Heat (J/kg)
Conductors, insulators and payback time
Materials that allow energy to spread through them quickly are called conductors. eg metals
Materials that allow energy to spread through them much more slowly are called insulators. eg wood, glass, air
Reducing heat loss in the home;
- fibreglass roof insulation
- reflective foil on walls and behind radiators
- Cavity wall insulation
- double glazing
- draught excluders
Payback time = how long it takes to pay for the insulation from the savings made.
eg Double glazing cost = £1800, Annual saving = £60, Payback time = 1,800/60 = 30 years
Conduction, convection and radiation
- the transfer of heat energy through a substance from the hotter region to the cooler region without any movement of the substance
- Happens in liquids and gases
- as the material gets hotter its particles move faster, causing it to expand and become less dense.
- it then rises up and is replaced by colder,denser liquid or gas
- transfer of heat energy by waves
- infrared radiation is emitted by hot objects
- can pass through a vacuum
- dark matt surfaces emit more radiation than light shiny surfaces at the same temp
- dark matt surfaces absorb more radiation than light shiny surfaces at the same temp
The electromagnetic spectrum
High frequency/short wavelength->G,X,UV,V,IR,M,R<-Low frequency/long wavelength
G,=gamma, used to treat cancers
X,= X-rays, used to produce shadow images of bones
UV,= Ultr-violet, can cause sunburn and damage living cells
V,= Visible, used to carry information via optical fibres
IR,= Infra-red,used to heat materials eg cooking and used in remote controls
M,=Microwaves , emitted from mobile phones, they are also absorbed by water molecules in foods, causing friction within the food to heat it up
R= Radio waves, used to transmit radio (and TV signals) between places
Refraction, reflection and total internal reflecti
Analogue and digital signals
Analogue signals vary continually in amplitude and/or frequency. They can have any value within a fixed range of values and are very similar to the sound waves of speach or music.
Digital signals do not vary, they have only 2 values or states on (1) or off (0). There are no values between. The information is a series of pulses. eg morse code.
Advantages of digital is that more information can be transmitted via optical fibres (multiplexing). Interference can easily be removed from digital signals.
Advantages of wireless signals;
- signals available 24 hours a day
- no wiring needed
- portable and convenient
- used for satellite communication
- transmitting radio & TV signals
Microwaves for communication;
- mobile phones use microwaves
- public concern over safety (not corroborated by science research yet)
- Needs line of sight between masts, so your mobile phone loses connection.
Light is a transverse wave
Stable Earth 2
When skin is exposed for a prolonged period to UV light it can cause sunburn or skin cancer.
Sun cream is effective at reducing damage caused by UV radiation. The higher the factor the lower the risk because high factors allow longer exposure without burning.
Safe Time = Recommended exposure time for skin type X Sun Block Factor
eg. Safe Time = 20 minutes X 2 = 40 minutes