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Reflection nebula. Planetary nebula. (This nebula is smaller and will only form a planet). Stage 2: Protostar. Gravity will slowly pull these particles together…. As they move inwards their gravitational potential energy is converted into heat and a PROTOSTAR is formed.
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Planetary nebula (This nebula is smaller and will only form a planet)
Stage 2: Protostar Gravity will slowly pull these particles together… As they move inwards their gravitational potential energy is converted into heat and a PROTOSTAR is formed
Stage 3: Main Sequence In a main sequence star the forces of attraction pulling the particles inwards are _________ by radiation pressure acting outwards due to the huge __________ inside the star. Stars are basically ________ reactors that use _______ as a fuel. During its main sequence a star will release energy by converting hydrogen and helium (light elements) into _________ elements. Our sun is an example of a main sequence star – it’s in the middle of a 10 billion year life span Words – heavier, balanced, hydrogen, nuclear, temperatures
Stage 4: Red Giant If the star is relatively small (like our sun) the star will become a RED GIANT If the star is big (at least 4 times the size of our sun) it will become a RED SUPERGIANT Eventually the hydrogen and helium will run out. When this happens the star will become colder and redder and start to swell…
Stage 5: The Death Red giant White dwarf Black dwarf What happens at this point depends on the size of the star… 1) For SMALL stars the red giant will collapse under its own gravity and form a very dense white dwarf:
2) If the star was a RED SUPERGIANT it will shrink and then EXPLODE, releasing massive amounts of energy, dust and gas. Before After This explosion is called a SUPERNOVA
The dust and gas on the outside of the supernova are thrown away by the explosion and the remaining core turns into a NEUTRON STAR. If the star is big enough it could become a BLACK HOLE.
Stage 6: Second generation stars Our sun is believed to be a “______ ______ star” – this is because it contains some __________ elements along with hydrogen and ________. These heavier elements would have been the products of a previous star that have been thrown out by a ________. These heavier elements are also found on planets, indicating that they might have been made from remains of previous _______ as well. Words – helium, heavier, second generation, stars, supernova The dust and gas thrown out by a supernova can be used to form a new star…
The formation of the universe The “Steady State” theory This theory states that the universe has always existed as it does now and hasn’t changed. The trouble is that the night sky would be completely lit up because of the billions of stars, but it’s not, so… The “Big Bang” theory This theory states that the universe started off with an explosion and everything has been moving away ever since. There are two main pieces of evidence for this: background microwave radiation and red shift. There are two main theories about how the universe started:
Microwaves When the “Big Bang” happened microwaves were produced and these are still reaching us now. They can sometimes be seen as TV interference.
Red Shift explained Source of light “Spectra”
helium If you pass the light through a gas something different is seen… Some wavelengths of light are absorbed by the gas – an “absorption spectrum”.
Before helium After If the light source is moving away the absorption spectra look a little different… helium
Before A similar effect happens with sound – this is called “The Doppler Effect” After Hear Doppler Effect The absorption lines have all been “shifted” towards the longer wavelength end (red end)… This is called red shift. The faster the light source moves the further its light will be “shifted”
Red Shift simplified Basically, if I walk towards you I’ll look slightly more blue. Then, if I walk away from you, I’ll look slightly more red!! Let’s try it…
This is the BIG BANG theory Light from different stars and from the edge of the universe also shows this “red-shift”. This suggests that everything in the universe is moving away from a single point.
Red shift summary Light from other galaxies has a longer _________ than expected. This shows that these galaxies are moving ____ from us very quickly. This effect is seen to a greater extent in galaxies that are _______ away from us. This indicates that the further away the galaxy is, the ______ it is moving. This evidence seems to suggest that everything in the universe is moving away from a single point, and that this process started around 14 _____ years ago. This is the ____ ________ Theory. Further evidence of this theory is Cosmic Microwave Background Radiation (CMBR) – this radiation comes from the Big Bang and fills the _________. Words to use – faster, away, universe, big bang, billion, wavelength, further
Big Bang Theory vs Steady State Some scientists have explained that red shift can actually be used to support the Big Bang Theory – this explanation is based around the rates of expansion and contraction of different galaxies. If our neighbouring galaxy is expanding at a different rate to the Milky Way then it will appear red or blue-shifted. However, the discovery of CMBR was the final nail in the coffin for the Steady State theory. So, Mr President, the Big Bang theory is now the widely accepted theory of how the universe began. Stephen Hawking, 1942 -
Ultrasound Ultrasound is the region of sound above 20,000Hz – it can’t be heard by humans. There are a number of uses for ultrasound: • Pre-natal scanning • Sonar • Communication between animals
Pulse-Echo techniques In pulse-echo techniques sound is reflected from an object to measure the distance to that object:
Pulse-Echo techniques - Ultrasound Ultrasound is the region of sound above 20,000Hz – it can’t be heard by humans. It can be used in pre-natal scanning, sonar techniques and as communication between _______: How does it work? Ultrasonic waves are partly _________ at the boundary as they pass from one _______ to another. The time taken for these reflections can be used to measure the _______ of the reflecting surface and this information is used to build up a __________ of the object. Words – depth, reflected, picture, medium, animals
The Maths of Pulse-Echo x Consider shouting at a wall: The speed of sound is given by: v = 2x/t Therefore x = vt/2
The Maths of Pulse-Echo 25 50 75 100 125 150 175 200 t/μs The echo takes 0.8 seconds to return and the speed of sound in water is 1500ms-1. How deep is the water? Use the ultrasound scan to determine the width of the amniotic sac and the width of the baby’s body. The speed of sound in the fluid is 1500ms-1 and in soft tissue the speed is 1560ms-1.
Using an oscilloscope with ultrasound 20ms/div Consider a block of metal with a flaw: Q. If the speed of the ultrasonic wave is 3,000m/s how far away is the flaw from the detector?
Infrasound Infrasound is the region of sound BELOW 20Hz (as opposed to ULTRASOUND which is above 20KHz) – it can’t be heard by humans. Some uses: • Communication between animals • African elephants use infrasound to communicate with other elephants many kilometresaway. • 2) Detecting movement in remote areas • 3) Detecting volcanic eruptions and meteors
The Structure of the Earth A thin crust - 10-100km thick A mantle – has the properties of a solid but it can also flow A core – made of molten nickel and iron. Outer part is liquid and inner part is solid How do we know this? These facts have all been discovered by examining seismic waves (earthquakes)
Seismic waves Earthquakes travel as waves through the Earth – we call them SEISMIC WAVES. There are two types: • P waves: • They are longitudinal so they cause the ground to move up and down • They can pass through solids and liquids • They go faster through more dense material • S waves: • They are transverse so they cause the ground to move from right to left • They ONLY pass through solids • They are slower than P waves • They go faster through more dense material
Seismic waves These P waves travel through the Earth and are refracted when they pass through a medium These P waves are being reflected at the crust These S waves cannot travel through the outer core as they only go through solids The paths of these waves are all curved because density is gradually changing
Locating Earthquakes By measuring the time it takes the wave to travel to these locations the location of the earthquake can be found.
Movement of the Crust These plates are moving apart from each other a few centimetres every _______ due to the ________ currents in the mantle caused by the ________ decay of rocks inside the core. The Earth’s _______ is split up into different sections called ________ plates: Words – radioactive, crust, convection, tectonic, year
Plate Movements Earthquakes and volcanic eruptions can be common here Igneous Rock Oceanic Crust Mantle Convection Currents Magma
Electric Current Note that electrons go from negative to positive and are “pushed” by the voltage + - e- e- Electric current is a flow of charge around a circuit By definition, current is “the rate of flow of charge”
Basic ideas… Electric current is when electrons start to flow around a circuit. We use an _________ to measure it and it is measured in ____. Potential difference (also called _______) is how big the push on the electrons is. We use a ________ to measure it and it is measured in ______, a unit named after Volta. Resistance is anything that resists an electric current. It is measured in _____. Words: volts, amps, ohms, voltage, ammeter, voltmeter
More basic ideas… If a battery is added the current will ________ because there is a greater _____ on the electrons If a bulb is added the current will _______ because there is greater ________ in the circuit
Electrical Power P V I Power is defined as “the rate of transferring energy” and is measured in units called “Watts” (W). The amount of power being transferred in an electrical device is given by: Power = voltage x current in W in V in A • How much power is transferred by a 230V fire that runs on a current of 10A? • An electric motor has a power rating of 24W. If it runs on a 12V battery what current does it draw? • An average light bulb in a home has a power rating of 60W and works on 230V. What current does it draw?
Fuels Coal, oil and gas are called “fossil fuels”. In other words, they were made from fossils. A “fuel” is something that can be burned to release heat and light energy. The main examples are:
Some definitions… A renewable energy source is clearly one that can be _______ (“renew = make again”), e.g. _____, solar power etc. A ___________ energy source is one that when it has been used it is gone forever. The main examples are ____, oil and gas (which are called ______ ____, as they are made from fossils), and nuclear fuel, which is non-renewable but NOT a fossil fuel. Words – non-renewable, coal, fossil fuels, wood, renewed
Using non-renewable fuels in power stations 1) A fossil fuel is burned in the boiler 2) Water turns to steam and the steam drives a turbine 3) The turbine turns a generator 4) The output of the generator is connected to a transformer 5) The steam is cooled down in a cooling tower and reused
Efficiency of Power Stations Heat Heat Heat 15J Boiler Turbine Generator 100J 50J 5J 85J 35J 30J Heat Kinetic Electrical
Pollution When a fuel is burned the two main waste products are _____ dioxide and ________ dioxide. Carbon dioxide is a _________ ___ and helps cause _______ _________. This is produced when any fossil fuels are burned. Sulphur dioxide, when dissolved in ________, causes ______ _____. This is mainly a problem for ___ power stations. Nuclear power stations do not produce these pollutants because they don’t ____ fossil fuels. Words – sulphur, coal, global warming, carbon, acid rain, greenhouse gas, rainwater, burn
Nuclear power stations The main difference is that the nuclear fuel is NOT burnt – it is used to boil water in a “heat exchanger” These work in a similar way to normal power stations:
Start up times Quick Slow Different power stations have different start up times: Gas Oil Coal Nuclear
Non-renewable energy sources Coal, oil, gas and nuclear Advantages Disadvantages Pollution – CO2 leads to global warming and SO2 leads to acid rain Cheap fuel costs Generate a lot of energy Fuel will run out Easy to use
