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Physics revision - Coggle Diagram
Physics revision
Radioactivity
Radiation Intro.
Henri Becquerel discovered that urnaium salts had caused his an imprint of his keys,as they were on top of them
He assigned Marie Curie to investigate futher, she stated that the uranium emits a radiation and the rate at which it does is known as radioactivity
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History of the atom
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In the 1800s John Dalton expanded on this stating that these atoms were tiny solid spheres and the different elements contained different solid spheres
JJ Thompson, disproved daltons prior theory he proved the existence of negatively charged particles(electrons
Thompson also issued his model which stated that the atom was a ball of positive charge with negative particles embedded in it
Ernest Rutherford wanted to test JJ Thompsons theory, he decided to fire alpha particles at a thin gold sheet, assuming Thompson was correct the positive paticles will just pass through and some might be reflected.
However, when he begun the experiment the particles went did get reflected but some were even deflected backwards, this caused Rutherford to claim that the atom was mostly empty space however the nucleus was very dense and positive which caused the alpha particles to be deflected
Neilhs Bohr was the epitome of the atomic model, he stated that the electrons didn't just randomly exist they orbited the nuclues and they did this at differet energy levels known as shells, THIS IS MOST LIKE OUR MODERN MODEL
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Alpha, Beta and Gamma
Alpha particles are strong but have little penetrating power and are usually stopped by air they are very ionising represented by Helium 2 protons 2 neutrons
Gamma particles are very penetrating but weak, they are barely ionising(they often pass straight through instead of ionising it) they can only be stopped by dense materials like concrete. They are waves of electromagnetic radiation.
Beta particles are basically fast moving electrons and have the same properties as them they are moderately ionising and moderatley penetrating (they can be stopped by 5cm of aluminium, for every beta particle emmited a neutron is converted to a proton
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If they collide with a atom, they can discharge it forming a positive ion
Nucleur decay equations
As alpha particles have 2 neutrons and 2 protons, in a decay equation you remove 4 from the mass number and 2 from the atomic number
Beta particles cause a neutron to be converted to a proton so the mass number stays the same however there is more protons than neutrons the atomic number increases. A fast moving electron is also emmited
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Radioactive decay
The process of decay is random and there is no controlling when it happens we can work out the total rate of decay by its activity. The decay occurs because of unstable isotopes emmiting radiation
Half life 2 definations - time taken for the number of radioactive nucleui to halve or the time take for the radioactive activity to halve.
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How radiation is harmful
Irridation is when an object or organism has been exposed to radiation this can then lead to radiation sickness, the types of radiation is general this includes ionising and non - ionising
Contamination is when the radioactive particles get on to other objects, contamination isn't deadly however it can result in decay which is harmful
Factors of radiation include: Location, The amount where abouts you have been exposed, Ionising radiation is the worst as it can pass through skin and cells and damage dna which can lead to cancer ultaviolet radiation can also cause this though
Gloves, Tongs and radiation proof clothing is needed as well as a steel lined box
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Radiation in medicine
Radiotherapy can be used to kill cancer cells, it can be placed either outside the tumor or next to the cancer cells. When its external gamma radiation is used as it is more penetrating through skin. When its internal beta radiation is used as its more damaging. Side effects can ensure like sickness and healthy cells can also die
Tracers - an unstable isotope will be placed in the body (injecting it or swallowing it) Then we can track it by the radiation it emmits and to see if the organs are functioning correctly. Isotopes with the shortest half life are used so the least amount of damage happens
Nucleur Fission/Fusion
Fission occurs either spontenously(rare) or when a neutron is added and the nuclues is split, adding a neutron to an already unstable nuclei will cause lots of energy to be produced and two daughter nucluei to be prodcued this occurs multiple times and is a chain reaction once neutrons are emmitied it can happen again
In nuclear reactors, control rods are placed which absorb neurtrons and slow down the reaction. The water is heated up by the energy released to produce steam which powers generators and turbines.
Uranium is cheap no harmful emmisions are released and there is a steady amount of energy available, however power plants are costly and nuclear waste is expensive
Fusion occurs in stars with the most common one being hydrogen fusing to get helium, it can't occur on earth and its the reason why all the elements past hydrogen exist. The two lighter elements fuse to form one heavier element and loads of energy is realeased E=mc^2
WAVES
Transverse waves
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Water waves and other electromagnetic radiation like visible light and ultraviolet are examples of transverse waves
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Space Physics
Life cycle of a Star
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Gravity makes the protostar more denser casuing the particles to collide more often this leads to an increase in temperature
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This is known as a main sequence star where the outward force from the fusion is balanced by the inward force of gravity
Main sequence exist until no more nucleur fusion can occur, then it becomes more dens and becomes smalller.
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Red giants expel their outer layers and become unstable this will lead it to become a White Dwarf which is a hot dense core this cools to become a Black Dward
Red Super Giants continue undergoing nuclear fusion for a while unti it explodes (supernova). This forms elements heavier than iron and expells them across the universe
Then either the supernova cools to form a dense region called a neutron star or it will collapse on itself forming a black hole which is so dense not even light can escape from it.
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Orbits
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Newtons first law is important here: 'every object will remain at rest or in uniform motion in a straight line unless compelled to change its state by the action of an external force.'
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This is because the speed is constant however the direction is constantly chaning and velocity is speed in a certain direction
The force of gravity works on the velocity of the object brininging it closer the gravitationl pull of the Earth on the moon is strong
If the moon was brought closer to the Earth the gravitational pull would increase this would mean that the moons orbit would need to be quicker so that it doesnt get sucked into the Earth
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Red Shift
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The wavelengths are spread out from the light emmited and this shows that the galaxies are moving away from us - this also increases its wavelnegth
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This is evidence for the big bang theory which states that the universe and space is expanding due to an increase in dark matter which increases the mass of the universe.
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The inverse of red shift exists where the light is squashed and wavelength decreases the light is shifted to the blue side - blue shift
WAVES (2)
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Speed of sound in air - You can measure it with this simple experiment. ( You will need two people a tape measure and a distance ruler to measure the distance between the two people)
1. Person 1 stands approximately 100 m away from Person
2 (use a meter ruler to measure this distance)
2. Person 1 makes an obvious noise and person 2 starts their watch when they see the sound being made and stop the clock when they hear the sound being made.
3. Speed of sound can be measured as speed = distance/time
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