TEMPERATURE
thermal equilibrium: 2 bodies in contact have no net heat flow
zeroth law of thermodynamics: if 2 bodies are in thermal equilbm w/ 3rd body > they are in thermal equilbm w/ each other
temperature: property of a body that decides whether it is in thermal equilbm w/ another body

establishing temperature scale
-choose thermometric subs
-select thermometric prop X [X- length, pressure, resistance, emf]
-ensure X continually varies w/ temp
-choose fixed (temp) pts [mp of ice, bp of water] [at std pressure] (pressure ^, mp decreases, bp ^)


from exp results: steam pt 100°C X_s t°C X_t ice pt 100°C X_i t/100 = (X_t - X_i)/(X_s - X_i) [assumed X varies linearly w temp]

Mercury in glass thermometer

thin capillary tube (bore): smaller for higher sensitivity (lower range)
large vol Hg bulb: more expansion per °C => more noticeable increase in Hg thread => lower range
thick glass wall: magnify Hg thread, make thermometer less fragile
thin bulb wall: fast heat conduction > quick response
mercury: expands uniformly, good conductor of heat, coloured, doesn't stick to glass wall

inaccuracy; not uniform bore, bulb shrinks after few years > affects 0 reading, not all Hg at same temp (only some in liquid)

Platinum-resistance thermometer

resistance of Pt increases / temp
t/100 = (R_t - R_i)/(R_s - R_i)
fine Pt wire wound on mica strip & connected to thick Cu leads
a pair of straight identical short-circuited dummy leads enclosed in same silica tube to compensate exactly for changes in R w/ temp of Cu leads to Pt wire

thermometer connected to Wheatstone bridge > adjusted until galvanometer reads zero => R_Pt = R
very sensitive, can't measure temp at a pt, expensive (Pt), slow response (large heat capacity)

Thermocouple

junctions made of 2 diff metal wires joined together kept at diff temp => small emf prod => I flow
thermo-emf depends on: type of metal, temp diff (emf proportional to temp change)
[emf-temp diff graph: always approx parabolic]
mercury-in-glass thermometer
-39 to 500°C
simple, direct reading, cheap, portable
not v.accurrate, small range, fragile

Pt-R thermometer
-200 to 1200°C
wide range, v.accurate, best for small steady temp diff
not suitable for rapidly changing temp (due to large heat capacity- slow response)

Thermocouple thermometer
-250 to 1500°C
wide range, fairly accurate, can measure -rapidly changing temp, -temp at pt
not as accurate as Pt-resistance thermometer within -200 to 600°C
thermometers based on diff property => diff values for same temp except at fixed pts where most agree by defn
disagreement due to assumption thermometric property varies linearly w/ temp (not true)

Absolute thermodynamic scale
defn depends on theoretical efficiency of perfectly reversible heat engine
theoretical scale => doesn't depend on property of subs
1K = 1/273.16 × triple pt of water [K: kelvin]
triple pt of water, T_tr: temp at which sat water vapor, pure water, ice exists at equilbm = 0.01°C = 273.16K

Ideal gas scale
ideal gas- obeys pV ∝ T exactly => pV/T = const [T in kelvin]
(pV)_t/T_t = (pV)_tr/273.16 => T = (pV)_t/(pV)_tr × 273.16
ideal gases don't exist; real gas like ideal gas at low p
temp given by ideal gas: identical to thermodynamic scale
T(K) = p_t/p_tr × 273.16 [vol = const]
using real gas: by extrapolating to zero => possible to measure ideal gas temp


Celsius temp scale
/°C = T/K - 273.15 [T: thermodynamic temp]
fixed pts: -273.15K, 0.01°C (T_tr)

centigrade	thermodynamic	celsius
*100°C	373.15K	100°C
	*273.16K	*0.01°C
*0°C	273.15K	0°C
-273.15	*0K	*-273.15°C

[*-denotes fixed pts]


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