physics 19.1 internal energy and temperature

2 ways in which energy transfer between 2 objects takes place

when one object exerts a force on the other object and makes it move = one object does work on the other object; one object is hotter than the other, so energy transfer by heating due to the temperature difference by means of conduction, convection, or radiation

the internal energy of an object

the sum of the random distribution of the kinetic and potential energies of its molecules - the energy of its molecules due to their individual movements and positions

thermal energy

the internal energy of an object due to its temperature

why would an iron bar that is magnetised have more internal energy than if it is unmagnetised

because of the magnetic interaction between the iron bar's atoms

2 ways in which the internal energy of an object is increased

energy is transferred by heating the object; or work is done on the object e.g. work done by electricity

2 reasons why the internal energy of an object stays constant

there is no energy transfer by heating and no work done; or energy transfer by heating and work done balance each other out

why does the internal energy of a lamp filament increase when the lamp is switched on

because work is done by the electricity supply pushing electrons through the filament, and so the filament becomes hot

what happens when a lamp filament reaches its operating temperature after the lamp is switched on

energy is transferred to the surroundings by heating, and the filament radiates light

why does a lamp filament radiate light and not continue to heat up after reaching its operating temperature

work done by the electricity supply pushing electrons through the filament is balanced by the energy transfer and light radiated from the filament

the first law of thermodynamics

when work is done on or by an object and/or energy is transferred by heating, the change of internal energy of the object = the total energy transfer due to work done and heating

a molecule

a group of atoms bonded together, and is the smallest particle of a pure substance that is characteristic of the substance

an atom

the smallest unit of matter, and is the smallest particle of an element that is characteristic of the element

what are the atoms and molecules held together by in a solid

by forces due to the electrical charges of the protons and electrons in the atoms

relationship between vibrations of molecules in a solid and temperature

the molecules in a solid vibrate randomly about fixed positions, and the higher the temperature of the solid, the more the molecules vibrate

why does a solid melt when the temperature is raised enough

because the solids molecules vibrate so much that they break free from each other and the substance loses its shape

what energy of the molecules of a solid increases when energy is supplied to raise the temperature of the solid

the kinetic energy of the molecules

what energy of the molecules of a solid increases when energy is supplied to melt the solid

the potential energy of the molecules, because the molecules break free from each other

the movement of molecules in a liquid

the molecules move about at random in contact with each other, because the forces between the molecules are not strong enough to hold the molecules in fixed positions

relationship between temperature of a liquid and the speed of its molecules

the higher the temperature of a liquid, the faster its molecules move

what energy of the molecules of a liquid increases when energy is supplied to the liquid to raise its temperature

the kinetic energy of the liquid molecules

why does heating a liquid further after an initial temperature increase cause it to vaporise

because the molecules have sufficient kinetic energy to break free and move away from each other

movement of molecules in a gas or vapour

the molecules move about randomly but much further apart on average than in a liquid

what effect does increasing the internal energy of a substance has

it increases the kinetic and/or potential energy associated with the random motion and position of its molecules

energy transfer by heating for any 2 objects at the same temperature

no overall energy transfer by heating will take place

thermal equilibrium

when two objects are at the same temperature and so no overall energy transfer by heating takes place

what the Celsius scale of temperature is defined in terms of

ice point = 0'C - the temperature of pure melting ice; and steam point = 100'C = the temperature of steam at standard atmospheric pressure

what the absolute scale of temperature is defined in terms of

absolute zero = 0K = the lowest possible temperature; and the triple point of water = 273.16K = the temperature at which ice, water, and water vapour co-exist in thermodynamic equilibrium

calculating temperature in 'C from absolute temperature in kelvins

temperature in 'C = absolute temperature in kelvins - 273.15

absolute zero

the lowest possible temperature - no object can have a temperature below absolute zero

internal energy of an object at absolute zero

an object at absolute zero has minimum internal energy, regardless of the substances the object consists of