chapter 14 - thermal physics

Question 1

triple point

Answer 1

3 phases of matter can exist in thermal equilibrium at this point
- water = 0.01ºC @0.64kPa

Question 2

thermal equilibrium

Answer 2

when two objects are in thermal equilibrium with each other there is no net flow of thermal energy between them
zeroth law - if 2 objects are in thermal equilibrium with a third then they are all in equilibrium eg A and C are in eq with B then A and C are in eq with each other

Question 3

absolute temperature

Answer 3

T(K) = θ(ºC) + 273
0K = -273ºC

Question 4

kinetic model

Answer 4

• all substances are made of atoms or molecules
• are arranged differently depending on phase

Question 5

solid

Answer 5

• regularly arranged, packed close together
• strong electrostatic forces of attraction holding atoms in fixed positions
• (can exhibit SHM - vibrate around equilibrium)

Question 6

solid to liquid

Answer 6

• solid is heated - atoms gain energy
• vibrate more rigorously (with increasing amplitude) and eventually break away from solid structure

Question 7

liquid

Answer 7

• atoms still close together + can change position, sliding over each other - more KE
• is still electrostatic forces between atoms but weaker so no fixed structure

Question 8

liquid to gas

Answer 8

• when heated atoms gain enough energy to break away

Question 9

gas

Answer 9

• atoms move much faster and are much further apart
• negligible electrostatic forces between them

Question 10

state change graph

Answer 10

temp against time
diagonal when heating flat when changing states
S>L is shorter than L>G as it taqkes more energy to turn liquid to gas than solid to liquid

Question 11

specific heat capacity of a block

Answer 11

• set up a block with insulation and heater in connected to ammeter and voltmeter with thermometer in block
• measure mass of block
• record initial temp of block
• insert heater when hot - make sure fully inserted so all energy is transferred
• time 300 secs - noting I and V at regular intervals (to record fluctuations)
• remove heater + measure maximum temp of block
  (wait for it to reach thermal equilibrium)
• IVt = mcΔT
• plot Tf against time
  Tf = (IV/mc)t + Ti

Question 12

specific heat capacity of block experiment errors

Answer 12

• I and V fluctuations
• mass error balance
• analogue thermometer
• heating of lagging
• immersion heater top heated

Question 13

internal energy

Answer 13

sum of randomly distributed KE and PE of the atoms or molecules in a substance
- increases by changing temp or state

Question 14

kinetic energy

Answer 14

movement energy ∝ T (K)

Question 15

potential energy

Answer 15

electrostatic intermolecular forces

Question 16

gas PE

Answer 16

0
- negligible forces between atoms

Question 17

liquid and solid PE

Answer 17

negative
- as energy has to be added to system to free them from bound state

Question 18

specific heat capacity

Answer 18

energy required to heat 1kg of substance by 1ºK
units - J/kgK
Q = mcΔT
- for all objects
- depends on form - ice or water is diff

Question 19

power

Answer 19

= E/t
= mcΔT/t = IV
IVt =mcΔT

Question 20

specific latent heat

Answer 20

2 types - fusion, vaporisation
Lf = specific latent heat of fusion
Lv = specific latent heat of vaporisation
Lv»Lf
Q = mL

Question 21

Latent heat of vaporisation experiment

Answer 21

• set up kettle connected to power meter and ac source on a balance with a timer
• water in kettle should be at 100ºC - reset power meter when steam appears
• video the experiment with timer and mass scale reading in frame
• record power and mass at time intervals
• plot P against change in m/t
  grad = Lv
  E = mL
  E/t = mL/t
  P = Lm/t

Question 22

Latent heat of vaporisation experiment errors

Answer 22

• water not at 100ºC - use less water - just covering heating element
• not just water heated - kettle is as well - lagging - warmer room so not much difference to surroundings

Question 23

brownian motion

Answer 23

all particles in a fluid move in random directions at high speeds
changes in direction are due to collisions

Question 24

observing brownian motion

Answer 24

smoke particles show random motion
- due to collisions with air particles

Question 25

how to prevent heat losses

Answer 25

lagging/ insulation
cover to prevent evaporation

Question 26

method of mixtures

Answer 26

• known masses of two substances at diff temps are mixed together
• allow to reach thermal eq and record final temp
• can find c of one if you know c of the other

Question 27

Latent heat of fusion experiment

Answer 27

set up a funnel filled with ice on top of a beaker
put a heater in the ice with a thermometer and connect to a current voltage circuit
- turn on for a given time
- measure the mass of water that is gained
Lf = IVt/m