thermal physics Flashcards
what is evaporation
when the more energetic particles near the surface of the liquid escape as they turn in to vapour. This decreases the average kinetic energy of the particles in the liquid which is directly proportional to the temperature of the liquid and thus the liquid cools down
what are the differences between evaporation and boiling
- evaporation occurs at all temperatures while boiling only occurs at a certain temperature
- evaporation is a surface phenomena while boiling i s a bulk phenomena
factors affecting rate of evaporation
- temperature
- surface area (larger better)
- draught (air movements better)
- humidity (lower better)
thermal expansion in states of matter
solid- little expansion, requires large amounts of energy
liquid - some expanison, some energy required
gases - lots of expansion, lots of energy required
application of thermal expansion
-liquid in bulb thermometer
-bimetallic strips
( extra room should be provided for solids to expand in railway tracks)
what is temperature
physical property that measures how hot or cold an object is
how to make a thermometer
- use fixed points of temperature (etc melting temperature of ice and boiling tmeperature of pure water) to work out the temperatures inbetween
properties of thermometers
- sensitivity
- range
- quick response time
- linearity
what is sensitivity of thermometers
-ability to detect a change in temperature, if the physical property changes greatly for a small change in temperature that indicates that your thermometer is sensitive
what is range of thermometer
difference between highest and lowest temperature a thermometer can measure
quick response time of thermometer
time taken for a physical property to detect and response to a change in temeprature
linearity
the chosen property varies linearly with temp throughtout its range, it changes at a steady rate
how to increase sensitivity of liquid in glass thermometers
- increase volume of liquid in the bulb
- decrease cross-sectional area of stem
how to increase range of liquid thermometer
use a longer tube
what is thermal capacity
the amount of heat energy required to raise the temperature of that object by 1c or the amount of energy given out by the object when it cools by 1c
formula for thermal capacity
energy required = thermal capacity x amount of temperature raised
what is specific heat capacity
the amount of thermal energy required to raise the temperature of 1kg of that substance by 1c
formula for specific heat capacity
thermal capacity = specific heat capacity x mass
formula for change in energy
change in energy = mass x specific heat capacity x change in temperature
what is latent heat
energy required to change the state of a substance (the energy required to break the bonds holding molecules together)
latent heat of fusion
energy required to turn a solid into a liquid
latent heat of vaporisation
energy required to turn a liquid into a gas
what is conduction
the main method of thermal energy transfer in solids
what is convection
the main way heat travels through liquids and gases
process of convection currents
- the molecules push each other apart, making the liquid/gas expand
- this makes the hot liquid/gas less dense than the surroundings
- the hot liquid/gas rises and the cooler surrounding liquid/gas moves in to take its place
- eventually the hot liqud/gas cools, contracts and sinks back down again
how does heat travel through a vaccuum
thermal radiation, the way heat reaches us from the sun
factors affecting infra-red emission
- the higher the temperature of the object the more radiation it will emit
- the larger the surface area of the object the more infrared radiation it will emit
