Advantages and Disadvantages of using photocells to provide electricity:
- low maintenence
- no need for power cables
- no need for fuel
- long life
- renewable energy resource
- no polluting waste
- no power at night or in bad weather
How light produces electricity in a photocell:
- energy absorbed by photocell
- electrons are knocked loose from the silicon atoms in the crystal
- electrons flow freely
The current and power produced in a photocell depends on:
- light intensity
- surface area exposed
- distance from light source
Advantages and Disadvantages of wind turbines:
- no polluting waste
- visual pollution
- dependancy on wind speed
- appropriate space and position needed
Why passive solar heating works:
- glass is transparent to Sun's radiation
- heated surfaces emit infrared radiation of longer wavelength
- glass reflects this longer wavelength infrared
An efficient solar collector must track the position of the Sun in the sky.
The dynamo effect can be increased by:
- using stronger magnets
- using more turns in the coil
- moving the coil faster
- moving the magnet faster
AC generators work by:
- coil of wire
- magnetic field
- coil and field are close
- there is a relative motion between the coil and field.
Electricity is generated at a conventional power station by:
- fuel is burned
- boils water to produce steam
- steam spins the turbines
- turbine turns generator
(Know how to use efficiency calculation)
Electromagnetic radiation at most wavelengths can pass through the Earth's atmosphere, by certain wavelengths, particularly infrared, are absorbed by some gases in the atmosphere.
Natural and man-made sources of greenshouse gases - methane, carbon dioxide, methane. These gases are produced when burnt.
- short wavelegth e-m radiation from the sun is absorbed by and heats the Earth.
- the Earth radiates heat as longer wavelength infrared radiation
- greenhouse gases absorb some infrared radiation, warming the atmosphere.
Global Warming 2
Human activity and natural phenomena both have effects on weather patterns including dust in the atmosphere:
- from factories reflecting radiation from the city back to Earth causing global warming.
- from volcanic ash and gases reflecting radiation from the Sun back into space causing cooling
Supports humans to blame:
- burning more fossil fuels+ amount of carbon dioxide in atmosphere increasing
- greenhouse gases trap heat and stop it from escaping into space
Refutes humans to blame:
- temp of earth changes over time
- increase in carbon dioxide not significant enough to change overall temperatures (see revision guide for more)
Global Warming 3
Some statements are evidence bases. This means they are based upon data gathered from scientific experiments, or on data collated from previous studies.
Some statements are opinion based. This means that they havent been tested scientifically.
Before data is universally excepted, it must be repeatable by other scientists, and verified as accurate.
Fuels for Power
(see revision guide for advantages and disadvantages of different types of fuel)
power = voltage x current
The unit of electrical energy supplied is the kilowatt hour.
energy supplied = power x time
Off peak electricity:
A - less demand for energy at night, cheaper for the consumer, avoids wasting electrical energy
D - inconvient to run appliances at night because of the noise they make
Fuels for Power 2
Why transformers are used in the National Grid to increase the voltage:
- electrical energy is transmitted at a high voltage to reduce energy waste and cost.
An increased voltage means a reduced current, so decreasing energy waste by reducing heating of cables.
Alpha - smoke detectors (most ionising, least penetrating)
Beta - some tracers and paper thickness gauges
Gamma - treating cancer, non-destructive testing, tracers and sterilising equipment. (least ionising, most penetrating)
- Alpha - stopped by a few sheets of paper
- Beta - stopped by a few mm of aluminium
- Gamma - mostly stopped by a few cm of lead
Nuclear radiation can form positive ions when electrons are lost from atoms.
Nuclear radiaiton can form negative ions when electrons are gained by atoms.
Ionisation can initiate chemical reactions.
Ionisation can damage healthy molecules in living cells, resulting in the death of a cell. This can also lead to cancer.
Uranium is a non-renewable resource.
- is a waste product from nuclear reactors
- can be used to make nuclear bombs
Advantages of nuclear power: cost is relatively low, power stations flexible at meeting demand, doesnt produce greenhouse gases, can reduce use of fossil fuels.
Disadvantages: radioactive waste active for a long time, storing waste is expensive, high maintenence costs and start up takes a long time.
Disposing of radioactive waste:
- low level waste in landfill
- encased in glass and left underground
Problems of dealing with radioactive waste:
- remains radioactive for a long time
- terroist risk
- must be kepy out of ground water
- acceptable radioactivity level may change over time
Stars - they can be clearly seen even though they are far away because they are very hot and give out light.
Galaxies - large groups of stars
Black holes - dense, dying stars with a strong gravitational field.
Circular motion requires a centripetal force.
Gravitational attraction provides the centripetal force for orbital motion.
A light year is the distance light travels in a year.
A light year is useful for measuring very large distances in space. For example, how far other galaxies are away or how big galaxies are.
Problems with manned spaced travel:
- planets are very far away and can take months or years to reach them
- fuel required takes up most of the spacecraft
- room must be found to store enough food, water and oxygen for the whole journey
- a stable artificial atmosphere must be maintained in the spacecraft.
- temperature outside is freezing so keeping warm is vital
- outside of the Earth's magnetic field, humans need sheilding from cosmic rays
- the low gravity effects peoples health
- radio signals take a very long time to reach earth
Unmanned spacecraft can withstand conditions that are lethal to humans.
Information from space is returned from different distances:
- distant planets - require information to be sent back
- nearby samples - can be brought back to earth for analysis
Advantages of using unmanned spacecraft:
- costs are lower as there is no need to provide space and provisions for humans
- with humans not on board, safety is no longer a consideration
- reliability has to be high as there would be no-one to fix any breakdowns
- instruments/equipment must require zero maintenance
Earth-Moon Collision Theory
A collision between two planets can result in an Earth-Moon system:
- the planets collide
- their iron cores merge to form the core of the Earth
- less dense material orbits as the Moon
Evidence for the Earth-moon system (collision theory):
- The Earth has a relatively large iron core but the Moon has a much smaller one.
- Moon rocks from the crust are similar in composition to rocks found on Earth.
- left from the formation of the Solar System
- they are in orbit between mars and jupiter.
Evidence for past explosions:
- layers of unusual elements in rocks
- sudden changes in fossil numbers between adjacent layers of rock
The asteroid belt between Mars and Jupiter is there because the gravitational attraction disrupts the formation of a planet.
- have highly elliptical orbits
- they come from objects orbiting the Sun far beyond the planets
- the speed of the comet increases as it approaches the sun
The speed of the comet increases as a result in the strength of gravity as it approaches the star (sun).
Near Earth Objects are observed with telescopes to determine their trajectory (path)
It is difficult to observe NEOs because they are smaller, darker than planets.
Reducing the threat of NEOs:
- surveys with telescopes to identify them as early as possible
- monitering by satellites
- deflection by explostions (when they are distant from earth)
The Big Bang
- most galaxies are moving away from us
- distant galaxies are moving away more quickly
- microwave radiation is recieved from all parts of the universe.
Big Bang Theory accounts for:
- light from other galaxies shifting to the red end of the spectrum
- more distant galaxies generally showing greaterred shift
- estimating the age and starting point of the universe
Life Cycle of a Star
- red giant
- planetry nebula
- white dwarf
- red supergiant
- neutron star or black hole (for massive stars)
Life Cycle of a Star 2
Life History of a Star:
- interstellar gas cloud
- gravitational collapse producing a proto star
- thermonuclear fusion
- long period of normal life (main sequence)
- end depends of mass of star
Properties of a black hole:
- large mass, small volume and high density
- strong gravitational attraction due to the large mass.
Theories of the Universe
- planets sat on spheres a fixed distance from the Sun
- stars were fixed on the outermost and didnt move
- sun was the centre of the universe
- earth rotated once every 24 hours
- the earth takes one year to resolve aorund the sun.
TELESCOPES - observed the moon - not a perfect sphere. Discovered four moons orbiting Jupiter. Venus had phases like the moon which meant that it couldnt have been attached to a crystal sphere, it orbited the sun.
Theories of the Universe
Technological advances contributed to new theories. Galileo was able to use more powerful telescopes. Copernicus didnt have this equipment and used mathematical analysis, astronomical observations and reviewed previous scientists.
Theories of both Copernicus and Galileo were not accepted at the time because they went against the church and the bible. (Catholic church thought that Earth was the centre of the Universe)