USEFUL (energy/power out) / TOTAL (energy/power in)
1 of 29
efficiency can be written in the form of either
a decimal or a percentage
2 of 29
the law of the conservation of energy
energy cannot be created or destroyed
3 of 29
good emitters and absorbers of thermal radiation
dark, matte surfaces
4 of 29
poor emitters and absorbers of thermal radiation
light, shiny surfaces
5 of 29
in terms of infra-red radiation, the hotter an object gets...
the more heat it radiates
6 of 29
the only form of energy transfer that does not need particles
infra-red (thermal) radiation
7 of 29
specific heat capacity is ...
the amount of energy required to raise the temperature of 1kg of a substance by 1 degree celcius
8 of 29
energy transferred in joules (E) =
m x c x temp. (Energy transferred in joules x mass in kg x specific heat capacity in j/kgdegreesC x temperature change in dgrees C
9 of 29
conduction takes place in...
a solid
10 of 29
convection takes place in...
fluids - liquids and gases
11 of 29
define conduction
the particles of a solid gain energy when heated, so they vibrate and collide with each other and transfer the heat energy by making those new particles move with energy
12 of 29
define convection
the particles gain energy when heated, so they move faster and thus move further apart, thus making them less dense - this means that they rise causing cooler particles to then gain more energy, so a circular current is made
13 of 29
define evaporation
the particles gain energy, so move further and further apart, and eventually they break off from the main body of liquid to become a gas
14 of 29
payback time =
cost of insulator / annuel fuel saving
15 of 29
define U values
they measure how effective a material is as an insulator
16 of 29
the lower the U value, the .... the insulator
better
17 of 29
what is sublimation
from a solid straight to a gas
18 of 29
the power of a device is measured in...
watts or kilowatts
19 of 29
power in watts =
joules per second
20 of 29
energy transfered in kilowatt hours (kW h) =
power in kilowatts x time in use in hours
21 of 29
total cost for running =
number of kilowatt hours used x cost per kilowatt hour
22 of 29
power stations produce electricity at a voltage of
25 000 volts
23 of 29
energy is supplied to home at a voltage of
230 volts
24 of 29
the network of cables that connect power stations to homes and buildings
the national grid
25 of 29
the national grid's voltage
132 000 volts (or more)
26 of 29
what does a step-up transformer do?
this increases the voltage from 25 000 volts to 132 000 volts before it is transported via pylons and cables
27 of 29
why does a step-up transformer increase the voltage?
because a higher voltage means a lower current, and it is the current that releases the energy, so a higher current means more energy lost
28 of 29
what does a step-down transformer do?
used in local sub-stations to decrease the voltage down from 132 000 volts to 230 volts so that the appliances in our homes can handle the voltage
Comments
No comments have yet been made