AQA Physics paper 2

• glass

  is more dense than air
• law of refraction

  when a light ray goes from a less dense medium to a more dense medium, e.g. air to glass, the ray bends towards the normal and slows down, and when a light ray goes from a more dense medium to a less dense medium, e.g. glass to air, it bends away from the normal and speeds up; also, rays in the same medium will be parallel to each other

  
• refraction

  light, radio waves, etc, being deflected in passing through the border between one medium and another or through a medium of varying density
• law of reflection

  angle of incidence = angle of reflection
• diffuse reflection


  the reflection of the light ray from the surface is reflected at many angles due to an uneven surface
• specular reflection


  the reflection of the light ray from the surface is at only one angle as the surface is smooth/flat
• reflection


  the throwing back by a body or surface of light, heat, or sound without absorbing it
• speed of light

  3 x 10⁸ m/s
• visible light


  the light that can be seen by humans, consists of the seven colours: red, orange, yellow, green, blue, indigo, violet - comes just after infraRED and just before ultraVIOLET, one use for it is in fibre optic cables, which carry data and work because of reflection of visible light - the light rays are bounced back and forth until they reach the end of the fibre
• infrared uses

  IR cameras detect IR and monitor temperature, so energy transfer from a house's thermal energy store can be detected using IR cameras
• infrared (radiation)


  infrared radiation (IR) is given out by all objects: the hotter the object, the more IR radiated - also, IR is stopped by the ozone layer
• microwave


  heh

  
• diffraction


  when a beam of light or other wave is spread out as a result of passing through a narrow aperture or across an edge
• radio wave


  have the longest wavelength and thus are used to transmit data over long distances, they can diffract around the curved surface of the earth
• EM spectrum, longest wavelength first

  Radio, Micro, Infrared, Visible, Ultraviolet (UV), X-ray, Gamma
• EM spectrum

  EM = electromagnetic, a group of all transverse waves, which don't require a medium to propagate (they can travel through a vacuum)
• wave speed (m/s)

  v

  = wavelength (m) X frequency (Hz)

  = λ (lambda) X f
• time period (s)

  t

  = 1 ÷ frequency (Hz)

  = 1 ÷ f
• time period


  number of seconds per wave, measured in seconds (d'oh)
• wavelength and frequency

  are inversely proportional to each other (if one increases, the other decreases, as they both equal the velocity, which doesn't change if they respectively increase and decrease inversely proportionally)
• frequency


  number of waves (past a point) per second, measured in Hertz; the higher the frequency, the higher the energy
• wavelength


  the distance from peak to peak or trough to trough
• amplitude


  the vertical distance between a peak/trough and the equilibrium point (middle line)
• longitudinal wave

  a wave where the direction of energy transfer is parallel to the direction of oscillation (direction of oscillation is side to side, back and forth)
• transverse wave


  a wave where the direction of energy transfer is perpendicular to the direction of oscillation (direction of oscillation is up and down)
• crumple zone


  area at the front of the car made to be crushed in the case of a crash and to take a lot of the impact
• adaptations of a car to reduce impact force if it crashes

  to reduce the impact force felt by those inside a car, it has 3 adaptations that increase the time taken for the crash to happen (meaning there is a bigger time to divide the momentum by, and thus reducing the impact force):

  1. seatbelts 2. airbags 3. crumple zone
• impact force

  F

  = change in momentum ÷ change in time

  = ΔP ÷ Δt
• explosion

  movement only after - after an explosion, the object cannot have any momentum as it had no momentum before
• collision

  movement before and after
• momentum (p) in kgm/s

  p

  = mass (m) in kg X velocity (v) in m/s

  = mv
• conservation of momentum

  in a closed system, total momentum before an event is equal to total momentum after the event

  Pbefore = Pafter
• factors that may affect braking distance (and thus stopping distance too)

  tyre treads, incline, icy road, rain, brakepads, speed of car, terrain
• factors that may affect thinking distance (and thus stopping distance too)

  fog, tiredness, alcohol, needing the toilet, distractions (e.g. phone), drugs, light level, reaction time
• braking distance


  distance travelled between putting your foot down on the brakes and the vehicle coming to a standstill
• thinking distance


  distance travelled between starting to think about braking and putting your foot on the brakes
• gravitational mass


  the mass of an object that gravity acts on
• explaining law 3

  for every action, there is an equal and opposite reaction - for example, take the flying motion of birds - a bird flies by use of its wings, and the wings push air downwards; since forces result from mutual interactions, the air must also be pushing the bird upwards - the size of the force on the air equals the size of the force on the bird; the direction of the force on the air (downwards) is opposite the direction of the force on the bird (upwards), and thus action-reaction force pairs make it possible for birds to fly
• a parachutists journey

  as she jumps out of the plane, the air resistance is little so the weight pulls her downwards, so she starts to accelerate - as she accelerates the air resistance increases until it is equal to her weight - this is when terminal velocity is reached as the two forces are balanced - when she opens her parachute, she decelerates as there is a much larger air resistance as the surface area has increased - eventually, the air resistance on the parachute decreases until it is the same as her weight - a new terminal velocity has now been reached, just slower than the last one - until she gets to the ground, where her weight is equal to the upwards force from the ground
• terminal velocity

  when the weight going downwards is equal to the air resistance going upwards