Physics P2

Physics P2

Motion
1. acceleration=V-U/T
2. F=Mxa
3. Speed=distance travelled in metres/time taken in seconds
4. Stopping distance-driver
  1. Braking distance-road,weather conditions
Work is done on an object when a force makes the object move
Electrons have a negative charge, when taken off the material it is left positive, but the resisting material is negative
Ohm's law states that the current through a resistor at constant tempreture is directly proportional to the potenial dfference across the resistor
Potential difference-a measure of the work done or energy transferred to the lamp by each coulomb of chrge that passes through it.
1. Unit of potential difference is volt (V)
Filament bulb: resistance increases with increase of the filament tempreture
1. Diode: 'forward' resistance low; 'reverse' resitance high
  1. Thermistor: resistance decreases if its temptreture increases
    1. LDR: resistance decreases if the light intensity on it increases
Mains electricty
1. Alternating currents repeatedly reverse their direction
2. A fuse contains a thin wire that heats up and lets if too much current passes through it.
  1. A circuit breaker is an electromagnetic switch that opens (i.e 'trips') and cuts the current off if too much current passes through it
Radioactivity
1. Gamma
  1. Stopped by thick lead and has an unlimited range in air
  2. Electromagnetic
  3. Weak ionising
  4. Not deflected by electromagnetic and magnetic fields
  5. Tracers in medicine- injected, the source needs a half life of a few hours, so the patient isn't exposed
2. Beta
  1. A neutron in the nucleus changes into a proton and an electron
  2. The electron created in the nucleus is instantly emitted
  3. The proton stays in the nucleus so the atomic number goes up by one and the mass number is unchanged. The electron is instantly emitted.
  4. Stopped by thin metal, a metre of air
  5. Thickness monitoring-in the manufacture of things, the source needs a half life of many years
3. Alpha
  1. Positive charge, because some of the alpha particles rebound, they must be repelled by another positive charge
  2. The nucleus loses 2 protons and 2 neutrons
  3. 2 protons and 2 neutrons are emitted as alpha particle
    1. The atomic number then goes down by 2
  4. Stopped by a few centimetres of air
  5. Smoke alarms-half life of several years
4. Radioactive decay is a random event-we cannot predict or influence when it happens
5. Isotopes-atoms with the same number of protons but different numbers of neutrons. Therefore they have the same atomic numbers.
6. Half life
  1. The average time it takes for the number of nuclei of the isoptopes in a sample to halve
  2. The activity of a radioactive source is number of nuclei that decay per second
  3. The number of atoms of a radioactive isotope and the activity both dercease by half every half-life
  4. Radioactive dating-we need a radioactive isotope that is present in the sample which has a half-life about the same as the age of the sample
Energy from the nucleus
1. Nuclear fission is the splitting of an atomic nucleus
  1. Release of 2-3 neutrons
  2. Happens when a neutron hits a uranium-235 nucleus or a plutonium-239 nucleus and the nucleus splits
  3. A chain reaction occurs
  4. Nuclear reactors: control rods absorb fission neutrons to ensure that, on average, only one neutron per fission goes on to produce further fission
2. Nuclear fusion is the process of forcing two nuclei close enough together so they form a single larger nucleus
  1. Energy is released when two light nuclei are used together
3. Nuclear issues
  1. Radon gas is an alpha emitting isotope that seeps into houses.
4. The universe was formed by hydrogen and helium
  1. Distance between stars is millions times greater than between planets
    1. The distance between galaxies is millions times greater than between stars within galaxies.
5. A protostar is a gas and dust cloud in space that can go on to form a star
  1. Low mass star:Protostar, mainsequence star, red giant, white dwarf, black dwarf
  2. High mass star: protostar, main sequence star, red super giant, supernova, black hole if sufficient mass
  3. The sun will become a black dwarf
  4. A supernova is the explosion of a supergiant after it collapses
  5. Elements as heavy as iron are formed inside stars as a result of nuclear fusion
    1. Elements heavier than iron are formed in supernovas, along with lighter elements
      1. The sun and rest of the solar system were formed from the debris of a supernova

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