Thermal Physics Flashcards
What is internal energy?
The internal energy of a body is the sum of the randomly distributed kinetic and potential energies of all its particles.
Do the particles in a body travel at the same speed. Explain.
All the particles in a body don’t travel at the same speed.
Some will be travelling faster than others - the speeds (and thus the kinetic energies) of the particles are randomly distributed. The majority of particles will travel at the average speed.
What does the distribution of particle speeds depend on?
The distribution of particle speeds depends on the temperature of the body. The higher the temp, the higher the average kinetic energy of the particles.
What is potential energy? How is it distributed across the particles in a body?
Potential energy is the energy a particle has due to its relative position. Like the kinetic energy of particles in a body, the potential energy of the particles are also randomly distributed.
What is a closed system?
A system that does not allow the transfer of matter in or out of the system.
What is the internal energy of a closed system?
The internal energy of a closed system is constant.
How can the internal energy of a system be increased?
- When work is done on the system (e.g moving its particles/changing its shape - applying a force).
- When temperature of system is increased.
- These changes causes the average kinetic energy and/or potential energy of the particles to change.
NOTE: No longer a closed system.
NOTE: when temeprature decreased or the system does work on something else, its
In a closed system internal energy is constant, but is the kinetic energy and potential energy of EACH particle the same?
Energy is constantly transferred betweeen particles within the system when the particles collide with each other, so the KE and PE of the particles is conctantly changing however, the total combined energy of ALL the particles i.e. internal energy remains constant.
If the internal energy of the system does change, what does that tell us?
The change of internal energy of the object = the total energy transfer due to work done and heating on the object if IE increases, or by the object if IE decreases. This is the first law of thermodynamics.
How does the internal energy of a substance change when the substances is changing state? (during the horizontal section of the graph line)
When a substance changes state, its internal energy changes because the potential energy of the particle changes but its kinetic energy (and temperature) remains the same.
*As discussed previously, when the temp of a substance is being increased through heating, the kinetic energy of the particles is increasing (as well as the potential energy), however when the substance reaches a certain temp it changes state, at which point the energy provided through heating is used to break the bonds between the particles, rather than to increase KE of particles.
Define specific heat capacity?
The specific heat capacity of a substance is the amount of energy needed to raise the temperature of 1kg of substance by 1K.
How to calculate specific heat capacity?
Energy change (J)= mass (kg) x specific heat capacity (Jkg-1K-1 x temperature
Q = mcΔT
*This equation shows why increasing temperature results in a change in internal energy.
What temperature is absolute zero?
Absolute 0 is a temperature of 0K/-273degrees
What is the internal energy for a system at absolute zero?
It has minimum internal energy.
How does the inversion tube experiment work?
A collection of tiny lead spheres in a tube. When the tube is inverted the spheres fall and hit the bottom of the tube. The gravitational potential energy of the spheres gets converted to the internal energy of the the spheres. Because there is a change in internal energy of the spheres there is a change in temperature, so by recording the change in temp and calculating the energy change for sing mgLn (where L is the length of tube and n is the number of inversions), as well as mass of tubes we can find the specific capacity of lead –> mgLn = mcΔT –> gLn = cΔT –> c = gLn/ΔT
