Conduction: particles gain kinetic energy, vibrate and energy is transferred throughout the metal.
Convection: transfer of heat through movement. In liquids and gases. Hottest particles rise and colder air goes to heat source- like a chain.
Radiation: transfer of heat through EM waves. NO particles involved. hotter the object, more radiation is emitted. DARK MATT SURFACES EMIT MORE radiation than light shiny surfaces. DARK MATT SURFACES ABSORB MORE radiation than light shiny surfaces.
Heat transfer in houses
Heat is lost in houses through conduction (WALLS, FLOOR, ROOF AND WINDOWS)
through convection (GAPS IN DOORS AND WINDOWS making heat rise up where it is LOST IN THE ROOF)
through radiation (WALLS, ROOF AND WINDOWS)
Percentages of heat loss:
- 25% ROOF
- 35% WALLS
- 15% FLOOR
- 15% DOORS
- 10% WINDOWS
Minimising heat loss in houses
ROOF: prevention: roof insulation- traps a layer of insulating air. POSITIVE: reduce heat loss by 20-25%, different methods NEGATIVE: expensive, needs to be laid by an expert
DOORS AND WINDOWS: prevention: draught excluders, double glazing, curtains POSITIVE: draught ex. reduce heat loss 15%, double gl. reduce 10%, draught ex and curtains= cheap & easy, NEGATIVE: air vents can't be blocked, double gl= expensive.
WALLS: prevention: cavity wall insulation + internat thermal boards POSITIVE: reduce heat loss 35% NEGATIVE: expensive
FLOOR: prevention: carpets/rugs, underfloor insulation POSITIVE: carpets/rugs easy to install NEGATIVE: underfloor insu= expensive
Only part of the energy produced is useful.
wasted and useful energy are transferred to surrondings NOT created or destroyed
efficiency= useful energy transferred/total energy supplied
e.g. light bulb= 100j/s in ~ useful: 20j/s (light) + wasted: 80j/s (heat) = 20/100 x100 = 20%
Becoming more energy efficient
SWITCHING LIGHTS OF WHEN LEAVING A ROOM: easy and simple BUT some people forget or don't like to be in a dark house.
ENERGY EFFICIENT LIGHT BULBS: cost less, less energy wasted and last longer BUT more expensive than normal bulbs.
USING ELECTRICAL EQUIPMENT AT NIGHT: cheaper than daytime BUT can be noisy therefore keeping people awake.
LETTING CLOTHES DRY NATURALLY: uses less electricity- less money BUT weather dependant.
TANKLESS WATER HEATER: water is only heated when needed- less energy is used to heat surplus + maintain heat BUT some units are not powerful enough for a normal household.
Types of Energy
Different types of energy:
- chemical (fuel, food and batteries)
- kinetic (found in any moving object)
- Electricity (easily transformed into thermal, light, sound and kinetic)
- Potential energy (strain/elastic like in elastic bands or gravitational)
- Thermal (heat)
In any process, the total energy before and after is the same.
The National Grid
Electricity is generated at power stations + distributed to homes, schools, facories etc. by a network of cables called the national grid.
Powerstations~step-up transformers~powerlines~step-down transformers~houses etc.
powerstations transmit a voltage of 25 000V to step-up transformers
Step-up transformers increase voltage + decrease current (400 000V) so that less energy is lost in transmission in wires
Electricity travels along the power lines at 400 000V (high voltage + low current)
at step-down transformers decrease voltage + increase current (230V) for consumption especially appliances.
- cannot be replaced; will eventually run out.
- to generate electricity from fossil fuels (coal, oil, gas) these are burnt, which boils water which produces steam which drives turbines which are connected to generators.
- nuclear fuels (uranium, plutonium) produce electricity by nuclear fission (collision of particles causing chain reaction producing huge heat energy) NOT FOSSIL FUEL
- to generate electricity from nuclear reactor generates heat from nuclear fission, heat exchanger transfers heat from reactor to the water which turns into steam which drives turbines.
ADVANTAGES: coal + nuclear are relatively cheap. All are flexible in meeting demand.
DISADVANTAGES: burning fossil fuels produces CO2 and SO2 which cause global warming. Oil is often carried on tankers risking spillages + pollution. Nuclear building and de-comissioning is expensive. Radioactive waste can stay dangerously radioactive for thousands of years- safe storage is expensive.
- nothing needs to be burnt to produce heat.
- wood is renewable because trees can be regrown quickly to replace those cut down.
- wind turbines harness wind to drive turbines which drive generators. usually on hills to get maximum wind.
- solar cells/panels made of semiconductors (silicon) which capture light energy + transforms it into electrical energy.
- hydro-electric dam: water stored in a reservoir above power station is allowed to flow down through pipes to drive turbines. produces a lot of power.
- tidal barrage: as tide comes in water flows through a valve freely. water is then trapped. At low tide, water is released through a gap with a turbine which drives a generator.
- nodding ducks are found in the sea. the motion of waves make them rock and movement is translated into a rotary movement which drives a generator.
- geothermal: in volcanic areas where hot water + steam rise naturally (due to radioactive decay in the earth). steam can be used to drive turbines which drive generators.
ADVANTAGES: For all, no fuel required, no pollutent gases required. Wind turbines need little maintenance + can be built offshore. Wind turbines, solar and tidal provide free energy once built. Tidal and hydro-electric are fairly flexible. Hydro-electric have a fast start up time. Solar is good on small scale + in remote places.
DISADVANTAGES: all apart from hydro-electric produce small amounts and are unreliable ( they depend on weather). all take up space. could be seen as unsightly. expensive to set up