Physics AQA P2 Additional Science

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  • Created by: Emma
  • Created on: 19-12-11 21:02


  • The steeper the line on a distance-time graph, the greater the speed it represents.
  • Speed (metre/second, m/s)= distance travelled (metre, m)

                                                             time taken (second, s)

  • Velocity is speed in a given direction.
  • Acceleration is change of velocity per second.
  • A body travelling at a steady speed is accelerating if its direction is changing.
  • The slope of the line on a velocity-time graph represents acceleration.
  • The area under the line on a velocity-time graph represents distance travelled
  • To carry out calculations involving:
  • The slope on a distance-time graph represents speed.
  • The slope on a velocity-time graph represents acceleration.
  • The are under the line on a velocity-time graph represents the distance travelled.
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Speeding up and slowing down 1

  • When two objects interact, they always exert equal and opposite forces on each other.
  • The unit of force is the newton.

Remember that if a body is accelerating it can be speeding up, slowing down or changing direction.  If a body is accelerating there must be a resultant force acting on it.

Rusultant force = mass x acceleration

(newtons, N) = (kilograms) x (metres/second)2

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Speeding up and slowing down 2

  • The thinking distance is the distance travelled by the vehicle in the time it takes the driver to react.
  • The braking distance is the distance the vehicle travels under the braking force.
  • The stopping distance = the thinking distance + the braking distance.
  • The weight of an object is the force of gravity on it.
  • An object falling freely accerlerates on about 10m/s2.
  • An object falling in a fluid reaches a terminal velocity.
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Work, energy and momentum 1

  • Work done = energy transferred.
  • Work done (joules) = force (newtons) x distance moved in the direction of the force (metres).
  • Elastic potential energy is the energy stored in an elastic object when work is done on the object.
  • The kinetic energy of a moving object depends on its mass and its speed.
  • Kinetic energy ) J = 1/2 mass x speed2.

                                                 (kg)         (m/s)2

  • Momentum (kg m/s) = mass (kg) x velocity (m/s).
  • Momentum is conserved whenever objects interact, provided no external forces act on them.
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Work, energy and momentum 2

  • Momentumhas size and direction.
  • When two objects push each other, they move apart with equal and opposite momentum.
  • The more time an impact takes, the less the force exerted.
  • Force (newtons) = change of momentum (kilogram metre/second)

                                                    time taken (seconds).

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Static electicity

  • Like charges repel; unlike charges attract.
  • Insulating materials that lose electrons when rubbed become positively charged.
  • Insulating materials that gain electrons when rubbed become negatively charged.
  • Electrical current is the rate of flow of charge.
  • A metal object can only hold charge if it is isolated from the ground.
  • A metal object is earthed by connecting it to the ground.
  • If a metal object gains too much charge, it will produce sparks.
  • A spark from a charged object can make powder grains or certain gases explode.
  • To eliminate staic electricity,

a. use antistatic materials, and b. earth metal pipes and objects.

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Currect electricty 1

  • Every component has its own agreed symbol.
  • A circuit diagram shows how components are connected together.
  • A battery consists of two or more cells connected together.
  • Resistance (ohms) = potential difference (volts)

                                               current (amperes)

  • The current through is a resistor at constant temperature is directly proportional to the potential difference across the resistor.
  • Filament lamp: resistance increases with increase of the filament temperature.
  • Diode: 'forward' resistance low; 'reverse' resistance high.
  • Thermistor: resistance decreases if its temperature increases.
  • LDR: resistance decreases if the light intensity on it increases.
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Current electricity 2

  • For components in series circuits:
  • a. the current is the same in each component.
  • b. the potential differences add to give the total potential difference.
  • c. the resistances add to give the total resistance.
  • For components in parrallel circuits:
  • a. the potential difference is the same across each component.
  • b. the total current is the sum of the currents through each component.
  • c. the bigger the resistance of a component, the smaller its current is.
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Mains electricity 1

  • Alternating current repeatedly reverses its direction.
  • Mains electricity is an alternating current supply.
  • A mains circuit has a live wire which is alternately positive and negative every sycle and a neutral wire at zero volts.
  • Cables consist of two or three insulated copper wires surrounded by an outer layer of flexible plastic material.
  • Sockets and plugs are made of stiff plastic materials which enclose the electrical connections.
  • In a three-pin plug or a three-core cable, the live wire is brown, the neutral wire is blue, the earth wire is yellow/green.  The earth wire is used to earth the metal case of  mains appliance.
  • A fuse contains a thin wire that heats up and melts, cutting the current off, if too much current passes through it.
  • A circuit breaker is an electromagnetic switch that opens (i.e. 'trips') and cuts the current off if too much current passes through it.
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Mains electricity 2

  • The power supplied to a device is the energy transfer to it each second.
  • Electrical power supplied (warrior) = current (amperes) x potential difference (volts).
  • An electrical current is the rate of flow of charge.
  • When charge flows through a resistor, electrical energy is transferred as heat.
  • Charge (coulombs) = current (amperes) x time (seconds).
  • Energy transferred (joules) = potential difference (volts) x charge flow (coulombs).
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Nuclear physics 1

  • alpha decay- nucleus loses 2 protons and 2 neutrons and 2 protons and 2 neutrons are emitted as an alpha particle.
  • beta decay- a nuetron in the nucleus changes into a proton and an electron is created in the nucleus and is instantly emitted.
  • Alpha particles in a beam are sometimes scattered through large angles when they are directed at a thin metal foil.
  • Rutherford used the measurements from alpha scattering experiments to prove that an atom has a small positively charged central nucleus where most of the mass of the atom is located.
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Nuclear physics 2

  • Nuclear fission occurs when a uranium-225 nucleus or plutonium-239 nucleus splits.
  • A chain reaction occurs in a nuclear reactor when each fission event causes further fission events.
  • In a nuclear reactor, one neutron per fission on average goes on to produce further fission.
  • Nuclear fusion occurs when two nuclei are forced close enough together so they form a single larger nucleus.
  • Energy is released when two light nuclei are fused together.
  • A fusion reactor needs to be at a very high temperature before nuclear fusion can take place.
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