phys unit 2

• brownian motion:

  1. rapid and random
  2. collisions w microscopic particles
  3. force applied
  4. random collisions = random movement
• temp = avg. k.e = avg. speed
• gases

  1. collisions (wall and molecules)
  2. exert pressure on container
  3. rebound off walls
  4. direction change
  5. velocity change
  6. momentum change
  7. force exerted
  8. force = change in momentum over time
• evaporation: the escape of more energetic particles from the surface of a liquid
• After molecules evaporate, the remaining molecules have a lower average kinetic energy (it cools)

  eg the body:

  -the liquid absorbs energy from the body so it can continue to evaporate
• increasing rate of evaporation:

  • increase temp (more higher energy particles)
  • increase surface area (more molecules at the surface)
  • draught/wind (molecules are removed before returning to the liquid)
• weaker intermolecular forces = greater expansion when heated
• • Conduction is a process that describes the transfer of heat through a solid by the COLLISIONS of higher energy particles with lower energy particles
• Gap between molecules is higher in liquids and gases than in solids. Since molecules are much apart from each other in liquids and gases, the amount of heat transfer by conduction is also less in liquids and gases when comparing to heat conduction in solids.
• so like basically

  A) glass

  B) water

  C) plastic

  D) rubber

  E) wood

  F) wool

  G) glass fibre

  H) plastic foam

  I) expanded polystrene

  
• raise your hand if you like CONVECTIONNN

  A) fluids

  B) heated

  C) flow

  D) hot

  E) less

  F) heated

  G) decrease

  H) density

  I) kinetic

  J) spread out

  K) volume

  L) cold

  M) denser

  N) sinks

  O) gravity

  P) displaces

  Q) rises upward

  R) cools

  S) increase

  T) lose

  U) closer

  V) less

  W) cool

  X) downwards

  Y) heated

  
• a convection current needs:

  1. a heat source
  2. a gravitational force
• thermal conduction

  • molecular lattice vibrations
  • movement of free (delocalised) electrons in metallic conductors
• thermal radiation

  • infrared radiation
  • all objects emit this radiation
  • does not require a medium
• The temperature of a body is linked to the balance between the amount of radiation absorbed and emitted.

  A) greater

  B) equal

  C) less

  D) absorption

  E) emission

  
• When visible light and high frequency infrared radiation are absorbed by the surface of the Earth, the surface gets hotter. Some of this energy is transferred to the atmosphere by conduction and convection.
• The Earth also radiates lower frequency infrared radiation. Some of this infrared radiation is transmitted through the atmosphere back out into space, and some is absorbed by greenhouse gases in the atmosphere. The greenhouse gases emit infrared radiation in all directions – some out into space and some back towards Earth, which is then reabsorbed.
• "what colour dishdasha should i wear in the desert??🤔🤔"

  what am i supposed to write here?

  A) best

  B) poorest

  C) best

  D) best

  E) worst

  F) worst

  
• black absorbs all energy and doesn't reflect any
• rate of emission of radiation depends on the surface temperature and surface area of an object
• Energy =mass x specific latent heat
• Change in thermal energy = mass x specific heat capacity (Jkg-1°C-1) x change in temp