P1.1 The transfer of energy by heating processes and the factors that affect the rate at which the energy is transferred Flashcards
How can heat be transferred?
Radiation, Conduction and Convection
What is heat radiation?
The transfer of heat energy by infra-red radiation
What do conduction and convection involve?
The transfer of energy by particles
What is conduction the main form of heat transfer in?
Solids
What is convection the main form of heat transfer in?
Liquids and Gases
What can infrared radiation be emitted by?
Solids, Liquids and Gases
What do all objects emit and absorb?
Infrared Radiation
The bigger the temperature difference…
The faster the energy is transferred by heating
Where is infrared emitted from?
The surface of an object
The hotter an object is…
The more infrared radiation it radiates in a given time
An object hotter than its surroundings…
Emits more radiation than it absorbs
An object cooler than its surroundings…
Absorbs more radiation than it emits
Which surfaces absorb and emit infrared radiation the best?
Dark, matt surfaces
Which surfaces are poor absorbers and emitters of infrared radiation?
Light, shiny surfaces
What do light, shiny surfaces do to infrared radiation?
They reflect it
What forces hold a solid together?
Strong forces of attraction
What arrangement does a solid have?
Regular and fixed
How much energy do particles in a solid have?
Not much
How do the particles in a solid move?
They vibrate around fixed positions
What forces hold a liquid together?
Weaker forces of attraction
What arrangement do the particles have in a liquid?
An irregular arrangement, the particles are close together but can move past each other
How much energy do particles in a liquid have?
More energy than particles in a solid
How do the particles in a liquid move?
In random directions at low speeds
What forces hold a gas together?
Almost no forces of attraction
What arrangement do the particles in a gas have?
None
How much energy do particles in a gas have?
More energy than liquids and solids
How do the particles in a gas move?
In random directions at high speeds, colliding into each other
What happens when you heat a substance?
You give the particles more kinetic energy
What is the process of conduction?
Where vibrating particles pass on their extra kinetic energy to neighbouring particles
Why is conduction faster in solids?
Because the particles are closer together and therefore will collide more often and pass energy between them
Why are metals good conductors?
Because of their free electrons which move through the metal colliding with particles and transferring energy
When does convection occur?
When an area gets hotter its particles move further apart, this makes that area less dense and lighter than its surroundings so it rises. When it starts to cool the particles move closer together and it falls
What is condensation?
When a gas cools turns into a liquid due to the particles losing kinetic energy
What is evaporation?
When particles in a liquid with the most kinetic energy overcome the forces of attraction and escape turning the liquid into a gas
What affects the rate of evaporation?
Temperature (faster if higher)
Density (faster if lower)
Surface Area (faster if larger)
Airflow (faster if greater)
What affects the rate of condensation?
Temperature (faster if lower)
Temperature of the surface that the gas touches (faster if lower)
Density (faster if higher)
Airflow (faster if less)
The bigger the surface area…
The more infrared waves that can be emitted/absorbed by the surface, so the quicker the transfer of heat
The smaller the volume…
The quicker the object will cool
What other factors affect the rate of heat transfer?
The type of material, the nature of the surface with which the object is in contact
The bigger the temperature difference between an object and its surroundings…
The faster the rate at which the energy is transferred by heating
What is the U-Value?
the rating to determine how good an insulator something is. The lower the u-value the better it is at insulating
What is Payback time?
The amount of time it takes to save back on your energy bills the money spent on the insulation
How do solar panels work?
They contain water that is heated by radiation form the sun
What is specific heat capacity?
The amount of energy needed to raise the the temperature of a 1kg substance by 2 degree
What is the word equation for specific heat capacity?
Energy = Mass x specific heat capacity x temperature range
