P1- Energy transfer by heating
Specific heat capacity
Heating and insulating buildings
Infared radiation
Conduction
Loft insulation
Aluminium foil
Thicker bricks
Cavity wall insulation
Double-glazing windows
between radiator panel and the wall and reflects radiation away from the wall, and reduces rate of energy transfer
fibreglass is a good insulator, as air between fibres reduces rate of conduction
2 glass panes with dry air or vacuum between. the thicker the glass and the lower the thermal conductivity, the slower the rate of heat transfer (air is good insulator and vacuum prevents conduction
insulation is pumped in the space between the 2 layers of brick, because it's a better insulator that air. traps air into small pockets reducing rate of conduction
lower thermal conductivity in external walls, so rate of energy transfer from inside to outside will be lower
amount of heat energy required to raise 1kg of a substance by 1 degree C
Heat energy transferred = mass x SHC x Change in temperature
E = mc
J = kg x J/kg degrees C x degrees C
The way heat is transferred through a solid
Heat is applied on 1 end and gives heat energy to the nearest particles
They vibrate more as a result
They knock into their neighbouring particles and give them some of their energy
This causes them to vibrate more and this continues through the length of the conductor
metals are the best conductors, because they have free electrons, so more collisions will take place
Greater thermal conductivity = transfers more energy per second by conduction than other materials
The thicker the material, the more insulating the material is
The lower the thermal conductivity of the material, the more insulating it is
Insulators transfer heat poorly
Good at trapping heat, as they have lots of trapped air
Air is a poor conductor, as particles are far apart
Can't transfer heat by convection, as it is unable to move
IR is a type of electromagnetic wave
Unlike visible light, you can't see IR
All objects give off IR, although hotter objects give off more
A dark surface emits and absorbs heat better than a light surface does
Shinier surfaces absorb heat poorly, as most IR is refelcted away
Matt surfaces absorb IR very well
A perfect black body is an object which absorbs all electromagnetic radiation that hits it
A good absorber is also a good emitter so black bodies are also perfect emitters of radiation
If an object absorbs more IR than it emits, its temperature increases
If an object emits more IR than it absorbs, its temperature decreases
If an object emits the same amount of radiation as it absorbs, the temperature stays the same
The sun emits all EM rays, including IR
The IR rays pass through the atmosphere and warm the surface of the Earth
The Earth emits low energy IR (long waves) rays to cool itself down
Some of the emitted IR is absorbed by greenhouse gases and traps the IR causing the Earth's temperature to rise, known as the greenhouse effect
Equations
W = F x s
work done = force applied x distance moved
Joules = Neutrons x metres
GPE = m x g x h
GPE = mass x gravitational field strength x height
Joules = kg x J/ kg m x metres
KE = 1/2 x m x v(2)
kinetic = 1/2 x mass x velocity or speed (squared)
Joules = 1/2 x kg x metres/second
EPE = 1/2 x k x e(2)
EPE = 1/2 x spring constant x extension x extension
Joules = 1/2 x n/m x metres
P = E/t
power = energy transferred / time
Watts = Joules / seconds
efficiency = (useful energy or power output / total energy or power input) x 100
Stores
Different energy stores
Chemical
energy transferred by chemical reactions
Thermal
Heat
Kinetic
The faster an object moves, the more KE it has.
Gravitational potential
you can increase an objects GPE by increasing its height off the ground
gravitational field strength on earth is 9.8 or 10
Elastic potential
EPE of an object can be increased by stretching or compressing it.
Spring constant is a number which shows how easy an object is to stretch. The lower the number, the easier to stretch
Transferred by
sound/light
heating
electric current
a force moving an object
Basics
Energy can't be created or destroyed, only converted from one store to another
Work
when you exert a force on an object and it moves a distance
One J of work is the amount of energy required to move an object 1m with a 1N force
Whenever an object does work against a force, some of its energy gets dissipated to the surroundings as heat
when the energy an object has is converted into a less useful form, the energy is said to have been dissipated to the surroundings
Efficiency
Some input energy is always wasted when it is making something work (dissipation)
The more input energy an appliance turns into useful energy, the higher its efficiency
Power
how much energy something transfers per second
1 Joule/second is 1 Watt