- Created by: Beth
- Created on: 04-05-11 10:48
Radiation & Conduction.
Thermal radiation: Is the transfer of energy by infra-red waves. These are part of the electromagnetic spectrum.
- All objects emit (give off) heat radiation
- The hotter the object the more heat radiation it emits.
- Heat radiation travels through space.
Radiation on surfaces: - Dark, matt surfaces are good absorbers of radiation. An object that is black and left in the sun will become hotter than the same object thats painted a shiny light colour. Dark matt surfaces are also good emitters of radiation. An object that is painted a dark dull colour will lose heat and cool down quicker than an object that is painted a shiny light colour.
Conduction: Occurs mainly in solids, liquids and gases are poor conductors. When end of a solid is heated, the particles at that end gain kinetic energy and vibrate more, this energy is then past on to neighbouring particles and in this way heat is transferred through the solid.
Convection and heat transfer.
Convection: Occurs in FLUIDS. When a fluid is heated it expands. The fluid then becomes less dense and rises. Warm fluid is replaced by cooler, denser fluid. The resulting convection current transfers heat throughout the fluid.
- Convection cannot happsn in solids.
- Type of surface makes no difference to the amount of conduction or convection from an object. Only affects radiated heat energy.
Heat Transfer: In a house, we want to minimise heat loss. By reducing losses due to conduction, convection and radiation.
- Conduction by using insulators (trapping layers of air.)
- Convection, preventing convection currents being set up (trapping air in small pockets.)
- Radiation by using light, shiny surfaces (poor emitters.)
Heat Transfer in a house.
- Loft insulation such as fibre glass reduces heat being lost throughthe roof.
- Cavity wall insulation reduces heat lost through the walls.
- Aluminium foil between a radiator panel and the wall reflects radiation away from the wall.
- A double glazed has 2 sets of glass, therefore has dry air between the panes. (Dry air is a good insulator so cuts down conduction)
Thermal: Flows from a hot object to a cooler object.
Sound: From a Radio/Voice.
Kinetic: Anything moving.
Nuclear: From nuclear reactions.
Electrical: Whenever an electrical current flows.
Gravitational Potential: Stored in any object that can fall.
Elastic Potential: Elastic bands.
Energy and efficiency.
The unit of energy is measures in "Joules" (J)
The less energy wasted by a device, the more efficient the device is.
Calculation to measure the efficiency: Efficiency=Energy transformed by the device
Efficiency can be measured in fractions or a percentage.
The power of a device is the rate at which it transforms energy.
The unit of power is the watt (W). A device with a power of 1W transforms 1J of electrical energy.
Often a watt is too small to be useful, so power may also be given in kilowatts (kW). 1kW = 1000W.
Power is calculated using this equation:
Power (W) = Energy transferred (J)
Time taken (Seconds)
The national grid.
In Britain, electricity is distributed through the National Grid. This is a network of pylons and cables that connects power stations to homes and other buildings.
POWER STATION-->STEP UP TRANSFORMER-->PYLONS-->STEP DOWN TRANSFORMER-->UNDERGROUND MAINS CABLE FOR BUILDINGS.
In power stations, the voltage is increased by the step-up transformers before the electricity is transmitted across the National grid. This is becuase transmission at high voltage reduces energy losses in the cables, making the system more efficient.
Energy from wind and water/power from the sun and
Energy from wind and water: We can use energy from wind and water to drive turbines directly. Electricity can be produced from energy obtained from falling water, waves or tides.
- Hydroelectric power stations: Water which has been collected in a reservoir is allowed to flow downhill and turn turbines at the bottom of the hill.
- In a wind turbine, the wind passing over the blades forces them to rotate and move the generator at the top of a narrow tower.
Power from the sun and earth: The sun produces energy that travels through space as an electromagnetic radiation. A solar cell can then convert this energy into electrical energy.
- Water flowing through a solar heating panel is heated directly from the sun.
- geothermal energy comes from energy released by radio active substances.
Energy and the environment.
Coal oil and gas are non renewable energy resources. This means that the rate at which they are used is a lot faster than the rate at which they are produced. If we continue to use these resources at the vast rate we are using them then they will soon run out.
- Fossil fuels produce greenhouse gases.
- Nuclear fuels produce nuclear waste.
- Renewable energy resources can affect plant and animal life.
Advantages and disadvantages of energy resources.
Coal/oil/gas: Reliable/Non renewable + Produces the greenhouse gas CO2
Nuclear: Reliable/Non renewable/high risk of accident like Chernobyl
Wind: Renewable + free/unsightly and noise and not reliable due to lack of wind
Falling water: Renewable + free/Only works in wet areas and risk of flooding
Waves: Renewable + free/can be harzadous to boats and isnt reliable
Tides: Renewable + free/ Only few esturies are suitable
Solar: Renewable + free + reliable in hot countries/Only generates small amount of electricity
Geothermal: Free + renewable/very expensive to build
P1B - Electromagnetic spectrum.
Electromagnetic radiations and magnetic disturbances: They travel as waves and move energy from place to place.
All of the waves travel at the same speed.
- Gamma rays have the shortest wavelength and highest frequency.
- radio waves have the longest wavelength and lowest frequency.
- Different wavelengths of electromagnetic radiation are reflected, absorbed or transmitted differently by different substances and types of surface.
- They travel through space at a speed of 300 million metres per second.
Gamma rays X-rays Ultra violet visible light Infra-red Microwaves Radio waves.
Electromagnetic spectrum (detail).
Gamma rays: Gamma rays are used to sterilise cells/bacteria, however they can also cause cancer.
X-rays: They are used to produce shadow pictures of bones, however can also cause cancer.
Ultra violet: Used for tanning and can also cause cancer.
Visible light: Photography, but can cause blindness.
Infra-red: Used for remote controls, however can burn and damage skin.
Microwaves: Used for mobile phones but also kills healthy cells.
Radio waves: Used for communication and there are no other dangers assosiated with radio waves.
Analogue and digital signals.
Communication signals are either analogue or digital.
- An analogue signal varies continuously in amplitude.
- Digital signals only have certain values, usually they are either high or their low. Low or high. There is no inbetween values in digital signals.
Alpha, Beta, Gamma.
- Alpha α: is a helium nucleus. Its made up of 2 protons and 2 neutrons.
- Beta β: Is a high speed electron from the nucleus It is given out (emitted) when a neutron changes to a proton and an electron.
- Gamma γ: Radiation is a very short wave length electromagnetic radiation.
We can measure the radioactivity of a sample of a radioactive material by measuring the count rate from it.
- Radioactivity of a sample decreases over time. The count rate depends on the individual material, some take 2 minutes some take 2 million years.
- We can sue the half life to measure how quickylu the radioactivity decreases. Its the time taken for the count rate from the original substance to half itself.
If a source of waves is moving relative to an observer, the wavelength and frequency 'seen' by the observer will have changed (shifted) from the original produced by the source.
This effect can be heard with sound waves. E.g: It is easier to hear when its moving towards you (red shift) and when it moves further away the sound decreases (blue shift)
Big Bang and looking into space.
Red shift shows us that distant galaxies are moving away from us and the furthest ones are moving the fastest.
The universe is now expanding outwards, this suggests that it started with a massive expolsion at a very small initial point. This is knows as the big band theory.
Telescopes are used to collect the visible light coming from the stars, and so see them. Telescopes are also used to collect radiation from other parts of the electromagnetic spectrum such as x-rays, or radio waves.