Chapter 14 - Thermal Physics

Question 1

What is the triple point of a substance?

Answer 1

The triple point of a substance is a specific temperature and pressure where all 3 phases of a substance can exist in thermal equilibrium

Question 2

How does energy behave at the triple point?

Answer 2

There is not net transfer of thermal energy between phases

Question 3

How does energy behave between hot and cold objects?

Answer 3

If one object is hotter than the other, there is net flow of thermal energy from the hotter object to the colder one

Question 4

What defines thermal equilibrium?

Answer 4

When two objects are in thermal equilibrium, there is no net flow of thermal energy between them

Question 5

What is the zeroth law of temperature?

Answer 5

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

Question 6

Why may the celsius scale be imperfect?

Answer 6

Celsius scale is compromised by how it is dependent on surrounding atmospheric pressure

Question 7

What does the celsius scale assume?

Answer 7

The celsius scale assumes atmospheric pressure is 1.01 x 10⁵Pa

Question 8

What constant temperatures do celsius and absolute temperature scale use?

Answer 8

Celsius scale uses 0^oC and 100^oC
Absolute temperature scale uses triple point off water and absolute zero

Question 9

What is the conversion between kelvin and celsius?

Answer 9

K = ^oC + 273

Question 10

What is Brownian motion?

Answer 10

Brownian motion is the random motion of particles suspended in a medium

Question 11

What laboratory practical shows Brownian motion?

Answer 11

Smoke particles are visible under a microscope
These particles move randomly caused by air molecules striking smoke particles
Mean KE of smoke particles is same as mean KE of air molecules

Question 12

How did Einstein explain Brownian motion?

Answer 12

Pollen grains and tiny water molecules
Collisions were elastic and resulted in momentum transfer from water molecules to pollen grains causing random bonds

Question 13

What is internal energy?

Answer 13

Internal energy is the sum of the kinetic and potential energies of atoms or molecules within a substance

Question 14

How does increasing temperature affect internal energy?

Answer 14

Increasing temperature increases internal energy as it increases average kinetic energy

Question 15

How do phase changes affect internal energy?

Answer 15

When a substance changes phase, the electrostatic potential energy increases significantly

Question 16

What happens to energy during a phase change?

Answer 16

The energy transferred to the substance does not increase temperature as it is transferred to increase potential energy

Question 17

How do the different phases have different potential energies?

Answer 17

Gases have no potential energy
Liquids have negative potential energy
Solids have a large negative potential energy

Question 18

What is the difference between energy required in boiling and melting?

Answer 18

Boiling requires more energy than melting as melting weakens bonds whereas boiling breaks the bonds

Question 19

What is the specific heat capacity?

Answer 19

Specific heat capacity of a substance is defined as the energy required per unit of mass to change temperature by 1K

Question 20

What is the formula for specific heat capacity?

Answer 20

E = c * m * T

Change in Energy = Specific Heat Capacity * Mass * Change in Temperature

Question 21

What is the formula for specific heat capacity using electricity?

Answer 21

c = IVt / mT

Specific Heat Capacity = Current * Voltage * Time / Mass * Change in Temperature

Question 22

What is the formula for latent heat capacity?

Answer 22

E = mL_FUS
E = mL_VAP

Question 23

What is latent heat capacity?

Answer 23

Energy required to change 1 kg of a substance to another phase

Question 24

How can a graph be used to estimate specific heat capacity?

Answer 24

E = c * M * T
For a given time ‘t’:
E/T = Mc T/t
P = Mc T/t
Energy supplied over given time against change in temperature over given time
Gradient = Mc so Gradient / m = c

Question 25

What is the method of mixtures?

Answer 25

Known masses of two substances at different temperatures are mixed together. The final temperature allows the specific heat capacity of one to be determined if the other is known

Question 26

How can the specific latent heat of fusion of water be determined?

Answer 26

Heating circuit with ammeter and voltmeter transfers energy to ice L_f = IVt / m

Question 27

What precautions need to be taken to measure specific latent heat of fusion?

Answer 27

Thermometer should ensure ice is at melting point Mass accurately measured Ice should just start to melt when heater turned on

Question 28

How can latent heat of vaporisation for water be measured?

Answer 28

Electric heater can be used with a condenser to collect and then measure the mass of liquid that changes phase L_V = IVt / m

Question 29

How to estimate the value for absolute zero using volume?

Answer 29

Attach ruler to capillary tube using elastic bands Boil water using kettle and pour into large beaker Place capillary tube with opening upward Measure water temperature Decrease temperature by 5 using cold water until reaches room temperature Draw graph of length against temperature Absolute zero = -c / m

Question 30

How to investigate the relationship between pressure and volume?

Answer 30

Measure syringe diameter Use plunger and draw in 5cm³ air Place tube over nozzle of syringe Set up clamp stand and attach syringe Attach string to plunger with mass Record volume for every additional mass Plot mg against 1/L * A