physics ocr gateway

• history of the atom

  1. John Dalton - solid spheres
  2. J J Thomson - plum pudding model, positive mass with negative particles dotted within it
  3. Rutherford - gold foil experiment, positive charged nucleus surrounded by negative particles
  4. Bohr - electrons exist in fixed orbits or shells
• density = mass/ volume
• how to measure density


  regular solid- find the volume and weigh the mass

  irregular solids- weigh the mass, use a eureka beaker and measure the water displaced which will be equal to the volume.
• change of states

  solid --> liquid - melting

  liquid --> gas - boiling

  gas <--> solid - sublimation

  gas --> liquid - condensing

  liquid --> solid - freezing
• specific heat capacity


  the amount of energy required for 1kg to be raised in temperature by 1 degrees celcuis change in thermal energy = mass x specific heat capacity x change in temperature
• specific latent heat


  the energy required for a change of state to occur

  thermal energy for a change in state = mass x specific latent heat
• pressure in gases


  pressure will increase when:

  temperature increases

  volume decreases

  pressure x volume = constant
• atmospheric pressure


  pressure is higher the closer to sea level you are because the weight of the air above pushes on the air below which compresses it. Temperature can also affect the density of the air.
• liquid pressure


  pressure due to a column of liquid = height of column x density of liquid x gravitational field strength
• scalars vs vectors


  scalars are just a magnitude (speed, distance, mass, time)

  vectors have both magnitude and direction (velocity, displacement, force, acceleration)
• accelerations is how quickly the velocity changes, it is measured in metres per second squared
• forces

  forces are both contact and non-contact

  resultant force is the overall force on a point or object
• an object is in equilibrium if all the forces on it are balanced
• newton's laws


  first - an object will remain stationary or at a constant velocity unless acted upon by an external force

  seconds - the force acting on an object is equal to its rate of change of momentum

  third - when two objects interact, the forces they exert on each other are equal and opposite
• momentum is a vector , all moving objects have momentum

  force= change in momentum/ time
• conservation of momentum


  in a collision when no other external forces act, momentum is conserved.

  momentum before = momentum after
• gravity is the force of attraction between all masses, the force due to gravity is weight. This means that an objects weight will change in different gravitational strengths while the mass will remain the same.
• collisions can be elastic or inelastic


  elastic - where the total energy in the kinetic energy of the objects colliding is the same before and after the collision

  inelastic - where some of the energy is transferred to other stores
• kinetic energy store

  kinetic energy = 0.5 x mass x speed^2
• when a force makes an object move, energy is transferred and work is done
• power is the rate at which energy is transferred as work done = energy transferred
• extension is directly proportional to force that the spring exerts on the mass.

  how much an elastically deforming object stretches for a given force depends on the spring constant

  the spring constant depends on the material, the stiffer the object the larger the spring constant.

  the relationship between extension and the force is called Hooke's law
• force and extension have a linear relationship which is Hooke's law, however, beyond a point this is no longer true which is the limit of proportionality.

  there is a limit to the amount of force you can apply to an object.
• moments


  a moment is the turning effect of a force

  moment = force x distance

  distance is the perpendicular distance between the pivot and the direction of the force

  total anticlockwise moment = total clockwise moment
• levers- transfer the turning effect of a force, they increase the distance from the pivot that the force is applied, so less force is needed for the same moment.

  they are known as force multipliers
• gears


  gears have circular cogs that can interlock so that gears cause the other to turn. As one gear turns clockwise the other will turn anticlockwise. The smaller the gear the faster it spins and the bigger the gear the slower it spins
• pressure in a fluid is transmitted equally in all directions and it caused a force at right-angles to any surface
• hydraulics

  a hydraulic system are used as force multipliers- a small force can be exerted on one piston to exert a larger force on the other piston to be able to move an object
• pre fixes


  giga- 10^9

  mega - 10^6

  kilo - 10^3

  centi - 10^-2

  mili - 10^-3

  micro - 10^-6

  nano - 10^-9
• static electricity


  static electricity builds up when electrons are transferred between things that rub together.

  if materials are conductors, the electron will flow back into or out of them so they stay neutral, static charge is only left on objects that have lost or gained electrons.

  electrically charged objects exert a force on one another.
• electric fields

  Electric charges have an electric field, show by field lines.

  Electric fields lines go from positive to negative and at a right angle to the surface of the object. The closer together the stronger the field and the stronger the force on a charged object.
• current- the rate of flow of electric charge around the circuit, this only flows through an electrical component if there is a potential difference
• resistance- the measure of how easily charge can flow
• circuit symbols

  cell

  battery

  switch (open and closed)

  lamp

  LED

  power supply

  fixed and variable resistor

  voltmeter

  ammeter

  diode

  LDR

  thermistor
• ammeter- measure the current flowing through the circuit

  must be put in series and can be put anywhere

  voltmeter- measures the potential difference across the component

  must be put in parallel with the component under test
• potential difference-current graphs


  resistors and wires- current is directly proportional to p.d.

  filament lamp- increasing the current increases the temperature which increases resistance so the graph is curved

  diode- current only flows in one direction in a diode so the diode has a high resistance in the opposite direction
• series circuits


  everything is in line

  potential difference is shared because energy transferred to the charges in the circuit by the power supply

  current is the same everywhere and is determined by the total p.d. and total resistance

  resistance adds up, it is the sum of all the individual resistances
• parallel circuits


  potential difference is the same across all branches because each charge can only pass down one branch of the circuit so it transfers all the energy

  current is shared between branches

  resistance is always less than that of the branch with the smallest resistance
• power is the rate of energy transfer per second, measured in watts (W)
• the bigger the p.d. the more energy to the circuit of every coulomb of charge