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Paper 5 Thermal phsyics
Temperature refers to energy that is supplied to an object. According to kinetic theory, this causes the particles in the object to move faster, increasing kinetic energy. In solids this would take the form of faster
vibrations, and in a gas, the particles would move much faster.
When all the kinetic energy is removed from an object, it reaches absolute zero. This occurs at 0 Kelvin or 273ºC i.e.
T k = T °C + 273
The intervals for both units are the same, i.e. the value of 1K is the same as 1ºC.
The increase in internal kinetic energy caused by heating becomes distributed throughout the object spreading from hotter areas to colder ones. This is because as particles vibrate, they collide with others and share
the energy. The energy at the hot parts is thus reduced, but increased at the colder parts.
The temperature increase of an object when energy is supplied is not always the same for different materials. This is dependent on the specific heat capacity. Specific heat capacity is defined at the energy required
to heat 1 kg of mass by 1 K. The change in temperature is dependent on the mass of the object, m, the energy supplied, E, and the specific heat capacity, c.
E = mc (J kg-1 K-1)
Internal energy is the sum of kinetic and potential energy of the molecules in a substance. The potential energy is due to bonds between molecules, and increases as they move further away from each other, e.g.
when a gas is heated, the particles spread out, increasing potential energy.
Not all molecules have the same kinetic and potential energy. It is randomly distributed according to the MaxwellBoltzmann distribution. This distribution shows the number of molecules at a given energy level.
i. There will be more molecules close to the average and fewer moving faster/slower than this.
ii. There are no molecules with zero energy.
iii. Only few molecules have high energies.
iv. There is no maximum energy a molecule can have.
The graph only represents one specific temperature. If there is a change in temperature, the graph will change: the peak will move towards higher energies.
The average speed of particles can be seen at the peak of the graph or as the rootmeansquaredspeed or r.m.s. speed. This is written as < c2 > and is directly related to average kinetic energy,
2 m < c > .
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The average kinetic energy is proportional to the absolute temperature of the gas.
1 < c2 > = 2
Where T is the temperature in Kelvin and k is the Boltzmann constant 1.38x1023 J K1. This equation proves that when the temperature is at absolute 0 there will be no internal energy.
Boyle's Law states that for a constant mass of gas at a constant temperature, the pressure exerted by the gas is inversely proportional to the volume it occupies i.e.…read more