Thermal Physics

Question 1

What is temperature

Answer 1

The measure of hotness of an object

Question 2

What is The triple point?

Answer 2

The specific temperature and pressure where solid, liquid, and gas phases coexist in thermal equilibrium. No net transfer of thermal energy between phases.

Question 3

What is the Zeroth Law

Answer 3

If two objects are each in thermal equilibrium
with a third, then all three are in thermal equilibrium with each other.

Question 4

What is Absolute Temperature

Answer 4

Absolute temperature scale uses water’s triple point and absolute zero; measured in kelvin (K), with increments equal to Celsius. Relationship: Kelvin = Celsius + 273. Kelvins are positive, with 0K as the lowest temperature.

Question 5

Describe the arrangements of solids

Answer 5

Atoms are closely packed together. Strong electrostatic forces of attraction between molecules. Molecules have kinetic energy, which allows them to vibrate around their fixed positions.

Question 6

Describe the arrangements of liquids

Answer 6

Molecules have a greater mean separation between each other than in solids. Molecules have more kinetic energy than solids, enabling them to change position and flow past each other.

Question 7

Describe the arrangements of gases

Answer 7

Molecules have greater kinetic energy than in liquids, are farther apart, and move randomly with negligible forces between them, only interacting upon collision.

Question 8

What is brownian motion

Answer 8

The molecules of a gas travel in random directions with random velocity. Can be seen by looking at smoke particles in air. The smoke particles are visible under a microscope, and exhibit random motion because of their collisions with the molecules in air, which result in a transfer of momentum in random ways.

Question 9

Why does volume increase as temperature increases

Answer 9

At higher temperatures, the average speed of particles increase. This increases the rate of collisions causing the substance to expand.

Question 10

What is the formula to calculate the spacing between molecules in a volume of a substance

Answer 10

Spacing = (Volume / Number of molecules) to the power 1 third.

Question 11

Define Internal energy

Answer 11

The sum of the randomly distributed kinetic and potential energies of atoms or molecules within the substance.

Question 12

How is internal energy increased?

Answer 12

Raising temperature increases internal energy and average kinetic energy of atoms or molecules. Phase changes, increase electrostatic potential energy.

Question 13

What happens during phase changes

Answer 13

During phase changes like melting or boiling, energy transfer increases electrostatic potential energy without raising temperature. Once the phase change completes, temperature rises as kinetic energy increases.

Question 14

What are the characteristics of a Temperature-Time graph

Answer 14

Temperature on Y axis
Time on X - Axis
Specific heat capacity calculated by Power / Mass * Gradient

Question 15

How to determine the specific heat capacity of a solid or liquid

Answer 15

Using a digital scale, measure the mass of the solid or liquid. Connect an electrical heater to a power supply, ammeter, switch and variable resistor in series. Connect a voltmeter to the electrical heater in parallel. Insulate the solid or liquid and place a thermometer to find its initial temperature. Place the heater in the solid or liquid and turn the switch on. Time how long the solid or liquid takes to increase in temperature by 10 degrees. Stir liquid to make temperature uniform. Calculate specific heat capacity using equation C = Current * velocity of heater * time taken / mass * 10.

Question 16

What is electrostatic potential energy?

Answer 16

Electrostatic potential energy relates to attractive or repulsive forces between charged particles. Negative values indicate attractive forces, requiring energy to separate particles. As distance between particles increases, it becomes less negative, reaching zero at infinite separation.

Question 17

What is specific heat capacity

Answer 17

Energy needed per unit mass to change temperature by 1K (or 1°C), with units Jkg-1 K-1.

Question 18

What is Specific Latent heat of fusion

Answer 18

The energy required per unit mass of a substance to change from solid to a liquid.

Question 19

What is Specific latent heat of vaporisation

Answer 19

The energy required per unit mass of a substance to change from liquid to a gas.

Question 20

Why Is it not possible to go lower than 0k

Answer 20

At 0k, the internal energy of a substance is at its minimum. The kinetic energy of all molecules are 0 and have stopped moving.

Question 21

Why is Latent heat of vaporisation usually higher than latent heat of fusion

Answer 21

There is a bigger difference in internal energy between a liquid and gas than between a solid and liquid.

Question 22

What is Molar Mass

Answer 22

The mass of one mole of a substance. The nucleon number of an element is the mass of one mole of that element in grams. Number of moles = Mass / Nucleon Number

Question 23

What are the assumptions of an Ideal gas

Answer 23

1) The gas has a large amount of molecules moving in random directions with random speeds

2) The molecules of the gas occupy negligible volume compared to the volume of the gas

3) Collisions between molecules and container walls are elastic

4) The time during collisions between molecules is negligible compared to time between collisions.

5) Electrostatic forces between molecules are negligible except during collisions.

Question 24

How does gas in a container produce pressure

Answer 24

Collisions between molecules and container walls are perfectly elastic, which means kinetic energy is conserved. Molecules rebound off container wall with the same velocity as before collision but in opposite direction: -v. Therefore the change in momentum is -2mv. Force = Change in momentum / Time during collision, therefore the wall exerts a force of -2mv/t on the molecule. According to newtons 3rd law, the atom also exerts an equal and opposite force on the container wall. Since a large number of atoms collide with the walls, a collective force is exerted on the cross sectional area of the walls, therefore the molecules exert pressure on the walls.

Question 25

What is boyles law

Answer 25

At a constant temperature, pressure of an ideal gas is inversely proportional to volume.

Question 26

What is the relationship between Pressure and temperature in an ideal gas

Answer 26

Directly proportional. p1v1/t1 = p2v2/t2

Question 27

What is the equation of state of an ideal gas

Answer 27

pressure * Volume = number of moles * 8.31 * temperature in kelvin

Question 28

Characteristics of a Pressure *Volume - Temperature graph

Answer 28

Gradient = number of moles

Question 29

What is the root mean square speed

Answer 29

Square the value of each speed given, then divide by how many speeds there are. This is the mean square speed - C bar ^2. Square root this value to get root mean square speed.

Question 30

What is the equation for pressure of a gas at the microscopic level

Answer 30

Pv = 1/3 number of molecules * mass of a single molecule * mean square speed

Question 31

What are the characteristics of the Max Boltzmann distribution

Answer 31

Particles in a gas move randomly, with velocities varying widely. The area under the graph represents the total number of molecules. As the gas temperature increases, the peak shifts to a higher speed and the distribution broadens.

Question 32

What is the boltsmann constant equation

Answer 32

Pressure * Volume = Number of molecules * 1.38 * 10^-23 * Temperature

Question 33

How to investigate boyles law in an experiment

Answer 33

Fill a sealed syringe with gas and connect it to a pressure gauge. Use the syringe to vary the volume of the container, and record the values for volume and pressure. When a graph of pressure against 1/volume is plotted, a straight line should be produced, showing a constant relationship. To increase accuracy in this experiment, the syringe should be lowered slowly so that no heat is produced from friction.

Question 34

How to estimate absolute 0

Answer 34

A sealed container of air, connected to a pressure
gauge, is placed in a water bath. The temperature of the water is varied, and the values of temperature and pressure and recorded. When pressure is plotted against temperature, a linear graph will be produced. At absolute zero, the gas molecules will have no kinetic energy, so
there will be no collisions with the container walls, resulting in there being no gas pressure. By
extrapolating the graph back the x intercept can be found, and this is equal to absolute 0.

Question 35

How is mean kinetic energy and temperature of an ideal gas related

Answer 35

The kinetic energy of gas molecules in an ideal gas is proportional to the temperature. Given by the equation 1/2 * mass of molecule * mean square speed.