Heat Flashcards
In what direction does heat energy flow
Heat energy always flows from hot to cold
State the energy transfer processes (heat)
Conduction
Convection
Infrared radiation
Evaporation
Condensation
What are the factors that affect the rate at which heat energy flows
The factors that affect the rate at which heat energy flows:
The temperature difference between the two objects
The surface area of an object
The colour of the object
What happens when the temperature of an object increases, in terms of internal energy
When the temperature of an object increases, the energy stored in the object increases (the object’s internal energy increases)
This is because heating causes energy to be transferred to an object’s particles, this increases the kinetic energy store of the particles causing them to move faster. This results in an increase in internal energy, which causes an increase in temperature
Complete the sentence
The energy stored in an object is called its ____________
The energy stored in an object is called its internal energy
Define internal energy
Internal energy is the total kinetic energy and potential energy of all the particles (atoms and molecules) that make up a system.
State the ways in which energy can flow
Energy can flow by:
Conduction
Convection
Infra-red Radiation
Condensation
Evaporation
Complete the sentence
The more delocalised electrons, _____________
Complete the sentence
The more delocalised electrons, the higher the rate of conduction
What does a high thermal conductivity mean in terms of energy transfer in a metal
The higher the thermal conductivity of a material, the higher the rate of energy transfer by conduction across that material
Define conduction
A method of energy transfer by heating where vibrating particles transfer energy through a material by colliding with neighbouring particles and transferring energy between their kinetic energy stores
In what type of material does conduction occur in
Conduction occurs in solids
What type of materials are the best insulators
Non-metal materials such as wool and fibreglass are the best insulators
What type of material is the best conductors
Metals are the best conductors
What is a fluid
A fluid is a gas or a liquid
Explain the process of conduction through metals
The metal has delocalised electrons
The delocalised electrons gain energy when the metal is heated and move faster through the metal.
The delocalised electrons collide with other electrons transferring kinetic energy to them.
This increases the internal energy of the metal causing an increase in temperature.
Explain the process of conduction through non-metals
The heat energy is conducted from the hot end of the object to the cold end of the object
It is transferred from atom to atom.
The atoms in the part of the object being heated vibrate faster and collide with each other more.
The collisions cause energy to be transferred between the atoms’ kinetic energy stores.
This process continues throughout the object until the energy is transferred to the other side of the object.
It is then usually transferred to the thermal energy store of the surroundings (or anything else touching the object)
Energy is transferred by conduction through the metal pan handle
Energy is transferred by conduction through the pan to the water
Why are all metals good conductors of heat (and electricity)
Metals have delocalised electrons.
These electrons can travel through the metal, transferring the energy more quickly
Why are metals better conductors of heat (and electricity) than non-metals
Metals have delocalised electrons.
These electrons can travel through the metal, transferring the energy more quickly
Non metals do not have delocalised electrons and pass on (transfer) heat energy by the vibrations of atoms. This process is very poor.
Define convection
Convection is a method of energy transfer by heating in liquids and gases in which energetic particles move away from hotter regions to cooler regions
Describe the process of convection
When the air/liquid is heated, the particles gain energy.
Therefore they move faster and their separation is further, causing a decrease in density.
Less dense and hotter air/liquid will rise above the more dense, colder air/liquid.
The cold, more dense air/liquid takes the place of the hotter, less dense air/liquid and the process continues
In what types of material does convection occur
Convection occurs in fluids (anything that can flow) - gas or a liquid
What is infra-red radiation
Infra-red radiation is the transfer of heat energy by an electromagnetic wave.
In terms of radiation, what do all objects do.
All objects continually emit and absorb infra-red radiation
Complete the sentence
Energy is _________ being transferred to and from ___________ (emitted and absorbed), even through empty space (a __________)
Complete the sentence
Energy is continually being transferred to and from objects (emitted and absorbed), even through empty space (a vacuum) - they do both at the same time
In terms of radiation, what effect does the hotness of object have
The hotter an object is, the more energy it radiates (the more infra-red radiation it emits in a given time)
In terms of radiation, what effect does the colour of object have
Dark matt surfaces emit and absorb more radiation than light shiny surfaces AT THE SAME TEMPERAUTRE
Which colours emit and absorb less radiation in comparison to other colours
Light shiny surfaces emit and absorb less radiation than dark, matt surfaces AT THE SAME TEMPERATURE
Which colours are good and poor reflectors and absorbers of infra-red radiation
Dark, matt surfaces are good absorbers and emitters (poor reflectors) of radiation
Light, shiny surfaces are good reflectors (poor absorbers and emitters) of infra-red radiation.
Why can infra-red radiation travel through a vacuum.
No particles are involved in the transferring of heat energy by infra-red radiation.
Metals have ____ thermal conductivity and transfer heat energy rapidly
Non-metals have a _______ thermal conductivity which is why they are used as insulators
Fluids have a _______ thermal conductivity
Metals have high thermal conductivity
Non-metals and fluids have a low thermal conductivity
Fluids have a low thermal conductivity
Why does conduction occur mainly in solids and not in liquids/gases
Conduction occurs mainly in solids as the particles in a solid are held together really closely which means there are lots of collisions that pass on the energy whereas in liquids and gases, the particles are all further apart and so they don’t collide as much
Why does convection occur mainly in liquids/gases and not in solids
Particles in liquids and gases are much more free to move around which is why they usually transfer energy by convection whereas in solids the particles are next to each other in fixed positions.
In terms of infra-red radiation explain how the temperature of an object can increase
The temperature of an object increases if it absorbs more infrared radiation than it emits
How does surface area affect the rate at which heat energy flows
The smaller the surface area of an object, the lower the rate at which heat energy is lost from an object by conduction and convection
How does the temperature difference between two objects affect the rate at which heat energy flows
The greater the temperature difference is between two objects, the greater the rate at which heat energy is lost from an object by conduction, convection and infra red radiation
In terms of infra-red radiation, what does a constant temperature mean
An object at a constant temperature emits infrared radiation at the same rate as it absorbs it
In terms of infrared radiation, what does an object that is hotter than it surroundings do.
An object that’s hotter than its surroundings emits more Infrared radiation than it absorbs as it cools down (e.g. a cup of tea left on a table
In terms of infrared radiation, what does an object that is cooler than it surroundings do.
An object that is cooler than its surroundings absorbs more infrared radiation than it emits as it warms up (e.g. a cold glass of water on a sunny day.
What do hot bodies mainly emit
Hot bodies mainly emit infra-red radiation
