Thermal Physics Flashcards
What equation links energy and specific heat capacity?
energy = mass x specific heat capacity x change in time
E = mcΔT
What is
specific heat capacity?
the amount of energy required to raise the temperature of 1kg of the substance by 1°C
What is energy measured in?
Joules (J)
What is mass measured in?
kilograms (kg)
What is specific heat capacity measured in?
joules per kilogram (J/kg)
What is temperature change measured in?
degrees Celsius (°C)
What is
latent heat?
the energy used to make/break bonds
How is latent heat calculated?
energy (required to change state) = mass x specific latent heat
E = mL
What is specific latent heat measured in?
joules per kilogram (J/kg)
Why does temperature plateau when a substance is heated?
because the heat energy is being used for weakening the bonds instead of increasing the temperature of the substance
and vice versa - as the bonds are strengthened they release energy
What are the two types of
specific latent heat?
latent heat of fusion (solid <> liquid)
latent heat of vaporisation (liquid<> gas)
Explain the
Evaporation Theory
- particles in a liquid are always moving
- they are moving at different speeds
- if a fast particle is close to the surface it might have enough energy to escape from the liquid
- (this is evaporation)
- because only the high energy particles have now escaped, the average energy of the particles which remain has decreased
- so the temperature of the liquid decreases
What can increase the rate of evaporation?
- increasing airflow
- increasing temperature
- increasing surface area
- decreasing humidity
What is the difference between evaporation and boiling?
- evaporation only happens at the surface of the liquid
- boiling happens throughout the liquid
- evaporation happens at any temperature
- bioling only happens at the boiling point
State the main conduction points
- it is energy not particles which move from high temperature to low temperature
- when particles have more energy they vibrate faster and bump into lower energy particles - transferring the energy
- solids are better conductors than liquids and gases because the molecules are closer together so there is a higher collision rate
State the main points about thermal conductors and thermal insulators.
- if a material is a good conductor of heat, the energy of the particles can be passed on easily
- in most good conductors, there are free electrons within the structure and these, as well as atoms, pass on the energy
- in insulators, there are no free electrons, so vibrations are passed on less easily
State the main points about convection
- convection is the transfer of thermal energy in a substance by the movement of the particles
- convection can happen in liquids and in gases but not in solids because the particles cannot move around
- hot air and hot liquid will rise because the particles gain energy so the fluid is less dense so the denser fluids sink and the less dense fluid rises
What are some examples of
convection?
- hot air balloons
- kettles
- radiators
- onshore winds
Explain how a wall reduces the unwanted energy transfers
- insulation is a poor conductor because it traps air
- air is a poor conductor
- insulation reduces convection by decreasing airflow/trapping air
Describe
absorbing radiation
- when energy from a high temperature object reaches a lower temperature object, some is absorbed
- dull black surfaces are better absorbers
- bright shiny surfaces are worse absorbers
Describe
emitting radiation
- the amount of energy emitted by and object depends on its colour, texture and temperature
- dull black surfaces are better emitters
- bright shiny surfaces are worse emitters
What is the law of
conservation of mass?
mass cannot be created or destroyed
What is a
perfect black body?
(physics)
An object that absorbs all of the radiation incident on it. A black body does not reflect or transmit any radiation.
What does the temperature of the Earth depend on?
- the rates of absorption
- the rates of emission of radiation or reflection
