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P2 (3) (Electrical Safety (Choosing the Right Fuse (Fuses are rated in…
P2 (3)
Electrical Safety
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Choosing the Right Fuse
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Fuse rating is too low = fuse melts even if the appliance works correctly. If it is too high, it won't melt is there is a fault
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Structure of Atoms
Electrons, Protons and Neutrons
Atomic number = number of protons in the atom, Mass number = number of neutrons and electrons
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Atom loses electrons = positive ion, Atom gains electron = negative ion
All atoms of the same element have the same number of protons but they could have different number of neutrons(isotopes)
Unstable atoms have different numbers of protons and neutrons(some will decay emitting ionising radiation from the nucleus)
Subatomic Particles
The model of the atom is evolving. scientists are looking for experimental evidence of unknown particles, and the force that hold them together
Radioactivity
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Nuclear Equations
Nuclear equations show how isotopes decay by emitting alpha and beta radiation(the proton number and mass number on each side must be balanced
Nuclear Radiation
Scattering Experiment
Plum Pudding model was an early of the atom(Rutherford ) 
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The pattern helped to explain the structure of an atom(Rutherford's nucleus model replaced the plum pudding model)
More Deflections
Alpha and Beta particles have opposite charges so they are deflected in opposite directions by electric and magnetic fiields
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Background Radiation
Natural and Lifestyle
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Natural Sources include rocks, soil and food
Sources are affected by lifestyle choices(eg on a long flight you increase your exposure to cosmic radiation)
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Half-Life
Measuring half-life
We cannot predict if a specific radioactive atom will decay, but we can predict how many atoms will decay in a sample in a given time
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After a time equal to two ha;f lives, the activity falls to a quarter of its original value
Each radioactive material has its own half-life, which varies from millions of years to milliseconds. The half-life does not change for a given material
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Using Nuclear Radiation
Using Radioisotopes
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Gamma rays kill living cells and penetrate materials so are used for sterilisation and cancer treatments
Beta radiation penetrates thin sheets of metal and cardboard so is sued to monitor the thickness of materials
Medical tracers are radioactive materials injected, inhaled, or eaten by a patient(used to identify blood flow, or identify blockages or tumours)
Alpha radiation is used in smoke detectors(particles ionise air so a current can flow, if smoke is absorbs the radiation, the alarm is switched on)
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Nuclear Fusion
Using Nuclear Fusion
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Very high temperature and very high pressures are needed for nuclear fusion because positively charged protons in nuclei repel each other
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Elements heavier than iron are produced during supernova(when massive stars explode releasing huge amounts of energy)
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Life Cycle of Stars
Main Sequence
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Nuclear fusion changes hydrogen to helium, and heavier nuclei(star is stable because forces are balanced within the star)
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When the nuclear fuel runs out, the star cools and becomes a black dwarf
A Matter of Size
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When its fuel is used up, the core collapses quickly and the star explodes as a supernova
After the supernova, stars up to 3 times heavier than the Sun become neutron stars. Heavier stars create black holes
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