Topic 3 - Thermal Physics Flashcards
Heat
Transfer of energy between a system and its surroundings.
Temperature
Temperature is a measure of the average kinetic energy of the particles in a system.
Internal energy
total kinetic energy plus potential energy
Potential Energy
Potential energy is the energy stored by an object
Specific Heat Capacity
The Energy needed to raise the temperature of one unit of mass of material by 1K
Specific Latent Heat
Energy per unit mass absorbed or released during a phase change
Latent Heat of Fusion
the amount of energy needed to melt or freeze the material at its melting point.
Latent Heat of Vaporisation
the amount of energy needed to boil or condense the material at its boiling point.
5 Features of an Ideal Gas
- The molecules take up negligible volume.
- All collisions between molecules and the walls of the container are completely elastic.
- no potential energy, only kinetic
- All molecules of a particular gas are identical.
- the molecules have constant random motion
Real Gas
Reals gases are non-ideal gases, whose molecules occupy space and have interactions.
What happens to potential energy during a phase change?
There is no temperature change, so only the potential energy between the molecules changes.
What are 3 conditions under which a real gas behaves similarly to an ideal gas
1) High temperature
2) Low pressure
3) Low density
What is the formula for power and how does it relate to Q (heat)?
Formula for power: energy/time , t = time (s)
Q/t = Power , therefore
mc(change in T)/ t = power
What is the formula involving pressure, area, and force?
p = F/A
If a fixed mass of ideal gas is kept in a -thermally isolated and sealed container- what does this mean for energy?
There is no energy change in the system.
Temperature and Internal energy are constant
What energy changes take place when a metal ball is released from rest and falls through a distance of h?
Initially the ball has gravitational potential energy and as it falls the energy is converted into kinetic energy and thermal energy.
What happens to temperature if average kinetic energy remains unchanged
We can deduce that temperature is also unchanged.
How to find the energy supplied by a heater during a given time period
Multiply the power output of the heater by the time elapsed
power = energy/time
7 assumptions of the kinetic model of an ideal gas
1) Newton’s laws of motion are obeyed by the gas particles.
2) Collisions are perfectly elastic.
3) No intermolecular forces act between the particles.
4) Gas molecules are considered point particles / have negligible volume.
5) The motion of the particles is random.
6) The duration of collisions is negligible
7) The effect of gravity is ignored.
Why does a decrease in temperature of an ideal gas cause the pressure to decrease?
Lower temperature means that the gas particles have less kinetic energy.
Less kinetic energy means decreased momentum and decreased force on the container walls during collisions.
Since p = F/A , and A (the area of the walls) does not change, pressure is reduced.
Distinguish between specific heat capacity and specific latent heat.
Specific heat capacity is the energy required to raise the temperature of one kilogram of a material by one kelvin.
Specific latent heat is the energy required to change the phase of one kilogram of a material without changing its temperature.
What happens to energy when two objects at different temperatures are in contact?
When two objects at different temperatures are in contact, the energy gained by the cooler object is equal to the energy lost by the warmer object.
What happens to the kinetic energy of an unpowered object as it moves from a lower point in a gravitational field to a higher point
Its kinetic energy is converted into gravitational potential energy.
