P2 Thermal physics

Question 1

What does CCR stand for

Answer 1

Conduction, Convection, Radiation

Question 2

Conduction

Answer 2

Transfers heat through direct contact + transfer/passing on of vibrations.
(best in solids)
Energy transferred through material from a warmer to cooler place Without the material itself moving

Question 3

Conduction in metals

Answer 3

Very good conductors - because they have delocalised electrons that are free to move.
These electrons carry thermal energy as they’re heated and move through the metal

The vibration of atoms + movement of electrons → metal transfer heat faster (good conductor)

Question 4

Conduction in non-metals

Answer 4

As the atoms vibrate (when heated), they collide with neighboring atoms , resulting each atom sharing its energy with neighboring atoms
Collisions (caused by vibration) transfer energy from the atoms hot end → cold end
Energy is steadily transferred down the object from hot to cold

Question 5

Conduction in liquid

Answer 5

Particles are close in contact with each other
Particles are free to move → vibration not passed on easily as in solids
Not a strong conductor

Question 6

Conduction in gas

Answer 6

Particles and very spread out + free to move
Gas is a very poor conductor of thermal energy

Question 7

Conduction efficiency

Answer 7

solid>liquid>gas

Question 8

Convection in liquids (e.g. water)

Answer 8

Water particles at the bottom are heated → expands
Water particles expand = increase in volume = decrease in density
Resulting water particles at bottom to rise at the top = water particles at the top sinks (as it is denser)
Heat is then transferred throughout the liquid

In Liquids (e.g., water): Heating causes expansion, decreasing density and making warmer water rise. Cooler, denser water sinks, creating a convection current that spreads heat.

Question 9

Convection in air (e.g. air balloons)

Answer 9

In Air (e.g., hot air balloons): Heating causes air to expand and become less dense, allowing it to rise and carry heat.

When air is heated → expand = density decrease
Dentistry decrease = it is less dense than surrounding air = floats up
For everything in a air balloon to rise = it must altogether have a lower density than the surrounding air

Question 10

Convection current examples in real life

Answer 10

Electric heater - thermal energy moves around the room from the heater as a result of convection currents rising from heater

Refrigerator - cold air sinks from the freezing compartment (at the top)
No hot food in the refrigerator

Question 11

Radiation

Answer 11

a form of thermal energy transfer that doesn’t require a medium to travel through (can travel through vacuum)
All objects emit infrared radiation
Hotter = more infrared radiation it gives out

Question 12

Characteristic of infrared radiation

Answer 12

Produced by warm/hot objects
Form of electromagnetic radiation
Travel through vacuum in a form of waves
Travel in straight lines
Warms objects that absorbs it
Invisible to naked eye
Can be detected by nerve cells in skin

Question 13

Good absorber and good emitters

Answer 13

Surface that is a Good reflector (shiny or white surfaces) = poor absorbers
Surface that is a Good absorber (matte black surface) = good emitter

Question 14

Factors affecting infrared radiation

Answer 14

1. An object hotter than its surrounding
   Object will radiate more energy per second that it absorbs = cool down
2. Object that’s cooler than its surroundings
   Object will absorb more energy per second than it radiates until it reaches the temperature of its surroundings

Question 15

Consequences of thermal energy transfer

Answer 15

Thermal energy travels from hotter to cooler place
Temperature difference makes the thermal energy flow

Question 16

Insulation

Answer 16

to keep energy in something that is hotter than its surroundings

Question 17

Home insulation methods

Answer 17

Curtains/draught excluders - stops convection current + prevent heat transfer

Loft & underfloor insulating materials - prevent conduction of heat through floor/roof

Double/triple glazing windows - vacuum between glass panes reduce loss/gain of heat by conduction/convection

Cavity walls - reduce heat loss/gain by conduction

foam/rockwool in wall cavity - furthers reduces heat transfer by convection

Question 18

Vacuum flask

Answer 18

Used to maintain temperature of the thing inside
Vacuum Flasks: Use glass and vacuum to prevent conduction and convection, with a reflective coating to reduce radiation loss.

Question 19

Car engine

Answer 19

Car Engines: Heat is transferred through convection, conduction, and radiation, and water is used to absorb heat due to its high specific heat capacity.

Question 20

Global warming

Answer 20

Global Warming: Greenhouse gases trap heat in the atmosphere, increasing global temperatures.
Earth is absorbing more infrared radiation than they emit

Question 21

Ocean current

Answer 21

Ocean currents: distribute thermal energy from the equator to the poles, balancing temperatures globally.

Question 22

Coat

Answer 22

Designed to prevent thermal energy loss by convection
Coast: trap air in padded layers (insulator) to prevent heat loss via convection, with reflective linings to retain body heat by radiation.