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Theme B — The Particulate Nature of Matter

B.1.3 Temperature Scales — IB Physics HL Revision Notes & Topical Questions

5 min read 9 parts Lesson 5 of 53 1 quiz

📚 IB Physics HL Hub / Topical Revision
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Curriculum Equation Key قوانين الرقم الهيدروجيني والاتزان الأيوني - pH & Acid-Base Equilibrium FormulasFast Exam Solution
pH = -log[H⁺] | pOH = -log[OH⁻] | pH + pOH = 14 | [H⁺][OH⁻] = 10⁻¹⁴
Word Equation & Conditions: الرقم الهيدروجيني = -لوغاريتم تركيز أيون الهيدروجين | pH + pOH = 14
Location & Specifications: الاتزان الأيوني، كيمياء 3 ثانوي، التحصيلي، و AP Chemistry.
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Lesson summary

B.1.3 Temperature Scales — IB PHYSICS SL notes: Convert between the Celsius and kelvin scales and explain the meaning of absolute zero and the fixed points.Temperature — a measure of how hot or cold an object is, related to the average random kinetic energy of the particles.Direc…

  • Direction of transfer
  • Not thermal energy
  • Liquid-in-glass thermometer
  • Other thermometric properties
  • Never negative
  • Conversion

Section 1 of 9What temperature measures

Temperature
  • Temperature a measure of how hot or cold an object is, related to the average random kinetic energy of the particles.
Direction of transfer
  • Direction of transfer thermal energy flows spontaneously from the object at higher temperature to the one at lower temperature.
Not thermal energy
  • Not thermal energy a bath of warm water holds far more energy than a hot spark but is at a lower temperature.

Section 2 of 9Celsius scale

1Fixed points
  • 0 °C for the melting point of ice and 100 °C for the boiling point of water at standard pressure.
2Interval
  • Interval it is divided into 100 equal degrees.
3Liquid-in-glass thermometer
  • Liquid-in-glass thermometer it assumes a linear relation between the column length and the temperature, calibrated at the fixed points.
4Other thermometric properties
  • Other thermometric properties the resistance of a thermistor, the e.m.f. of a thermocouple and the pressure of a gas at constant volume.

Section 3 of 9Kelvin scale and absolute zero

Kelvin
  • Kelvin the SI unit of temperature, quoted with the symbol K and no degree sign.
Absolute zero
  • 0 K or −273 °C, the lowest possible temperature.
  • It is defined as the temperature at which the particles have zero kinetic energy (minimum energy).
  • No more energy can be removed from a system at 0 K.
Never negative
  • Never negative a temperature in kelvin cannot be negative.
Space
  • Space the temperature of empty space is about 2.7 K.

Section 4 of 9Converting between scales

Conversion
  • T/K = θ/°C + 273 and θ/°C = T/K − 273.
  • The exact offset is 273.15, but the data booklet uses 273.
Equal divisions
  • Equal divisions a change of 1 K equals a change of 1 °C.
Values
  • Values water freezes at 273 K and boils at 373 K, 20 °C is 293 K and room temperature of 300 K is 27 °C.
Remembering
  • Remembering the data booklet lists the conversion under unit conversions.

Section 5 of 9Choosing and using a scale

Use kelvin
  • Use kelvin for equations where temperature is a multiplier or in a ratio.
  • pV = nRT, Ek = (3/2)kBT and L = σAT4 are examples.
    What the symbols mean: p = pressure (Pa) · V = volume (m3) · n = amount of gas (mol) · R = 8.31 J mol−1 K−1 · T = temperature (K = °C + 273)
Either scale
  • Either scale when only a temperature change ΔT matters, as in Q = mcΔT.
Equal changes only
  • 20 K is the same change as 20 °C, but a temperature of 20 K is not 20 °C.
Why absolute
  • Why absolute a value in °C would give wrong ratios in gas laws and radiation laws.
Definition
  • Definition the kelvin is defined by fixing the Boltzmann constant, kB = 1.38 × 10−23 J K−1.

Section 6 of 9Thermometers

ThermometerAdvantagesLimitations
Liquid-in-glassCheap and directLimited range, slow, cannot be read remotely
ThermistorRapid response, high sensitivity, can be loggedNarrow range, non-linear
ThermocoupleVery wide range, fast because of small massNeeds a reference junction
Gas thermometerAccurate and defines a scaleBulky
Equilibrium
  • Equilibrium the thermometer must reach thermal equilibrium with the object.
Small heat capacity
  • Small heat capacity so that it does not change the temperature it measures.
Choosing
  • Choosing compare range, sensitivity, response time and whether it disturbs the system.
Calibration
  • Calibration repeat at fixed points.

Section 7 of 9More from the specification

1
Calibrating thermodynamic temperature scales
  • Calibrating thermodynamic temperature scales referencing fixed ice points and boiling points on Earth establishes empirical Celsius and thermodynamic Kelvin scales.
2
Absolute Temperature and Molecular Kinetic Energy
  • Absolute temperature in kelvin (K) is a direct measure of the average random translational kinetic energy of molecules within a substance, defined by Ek = (3/2) kB T.
3
Kelvin and Celsius Temperature Scales
  • Temperature scales are related by T(K) = theta(degrees C) + 273.15,
  • where absolute zero (0 K) represents the lowest theoretical temperature at which particle thermal kinetic energy is minimal.
4
Specific Heat Capacity versus Latent Heat
  • Specific heat capacity c measures the energy needed to raise the temperature of 1 kg of a substance by 1 K (Q = mc delta_T),
  • whereas specific latent heat L governs phase changes at constant temperature (Q = mL).
    What the symbols mean: E or Q = energy to change state without a change of temperature (J) · m = mass (kg) · L = specific latent heat (J kg−1)
5
Conduction, Convection, and Radiation
  • Thermal energy is conducted through solids via lattice vibrations and free electrons, convected through fluids by bulk circulation,
  • and radiated across empty space as electromagnetic waves.
6
Potential energy
  • Energy stored by the configuration of a system.
7
Wavelength
  • Distance between a point on one wave and the same point on the next wave
8
Solid
  • State with a fixed shape and a fixed volume.
9
Fusion
  • Joining of light nuclei into a heavier one.
10
Intensity
  • Power per unit area perpendicular to the wave direction.
11
Apparent brightness
  • The power received per unit area at the observer
12
Phase change
  • Change of matter from one state to another
13
Thermal conductivity
  • Material constant relating the rate of conduction to the temperature gradient and area
14
Surface temperature
  • Effective temperature of the star's radiating surface.
15
Copper
  • Metal widely used for electrical wires.
16
Convection
  • Transfer of thermal energy by the movement of a heated fluid
17
Conduction
  • Transfer of thermal energy by lattice vibrations and free electrons
18
Molecule
  • Tiny particle of the fluid, too small to be seen.
19
Luminosity
  • The total power of radiation emitted by a star.
20
Density
  • Mass per unit volume.

Section 8 of 9Key terms

TermMeaning
TemperatureMeasure of how hot or cold an object is; related to average random kinetic energy
Absolute zeroLowest possible temperature, 0 K or −273 °C
KelvinSI unit of temperature
Fixed pointReference temperature such as the melting point of ice
Thermometric propertyPhysical property that varies with temperature and is used in a thermometer
Boltzmann constantkB = 1.38 × 10−23 J K−1

Section 9 of 9Exam technique

1
Writing the conversion with the wrong sign — add 273 to go from °C to K.
2
Using °C in gas-law equations — use kelvin.
3
Writing a degree sign with kelvin — it is K, not °K.
4
Saying 20 K is 20 °C — only the changes are equal.
5
Confusing temperature with thermal energy — temperature is about average kinetic energy.

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