University:
Concordia University Wisconsin
Course:
PHYS 1524 | General Physics II
Academic year:

2023
Views:

331

Pages:

3
Author:

ilikemyicons0y5

THERMAL PROPERTIES OF MATTER THERMAL SCALE & THERMAL EXPENSION 1. TEMPERATURE SCALES Name of the scale Celsius Symbol for each degree °C Lower fixed point (LFP) 0°C Upper fixed point (UFP) 100°C Number of divisions o n the scale 100 Fahrenheit °F 32°F 212°F 180 Kelvin K 27 3.15 K 373.15 K 100 C  0° F  32° K  2 73 .1 5 X–LFP = = = 1 00°  0 ° 21 2°  3 2° 3 73.15  2 73 .1 5 UFP–LFP  ΔC ΔF ΔK ΔX = = = 100 180 100 UFP – LFP (i) Old thermometry X – X0 θ–0 = [two fixed points – ice & steam points] 100 – 0 X100 – X 0 where X is the thermometric property i.e. length, resistance etc. (ii) Modern thermometry T–0 X = 273.16 – 0 X tr [Only one reflection point – triple point of water is chosen] 2. THERMAL EXPANSION In solids  Linear expansion = 0 (1 + ) In solids  Areal Expansion A = A0 (1 + ) In solids, liquids and gases  volume expansion V = V0 (1 + ) [For isotropic solids :  :  :  = 1 : 2 : 3] Thermal expansion of an isotropic object may be imagined as a photographic enlargement. For anisotropic materials  xy = x + y and  = x + y + z T2 l  If  is variable : 3. l 0 dT T1 Application of thermal Expansion in Soli (a) Bi–metallic strip : Used as thermostat or auto-cutin electring heating circuits) Brass Steel Room temperature (b) Simple Pendulum : T  2 l g Steel Brass Higher temperature (Q T  l  T 1 l  ) T 2 l T 1 =  T 2 (c) Scale reading : Due to linear expansion / contraction, scale reading will be lesser / more than actual value. If temperature  then actual value = scale reading (1 + ) Fractional change in time period THERMAL PROPERTIES OF MATTER (d) Thermal Stress Heating (Compressive Stress) Thermal strain = Δl = l As Young’s modulus Y  4. F/A l / l ; So thermal stress = F=YA Thermal expansion in liquids (Only volume expansion) a  γr = Apparent expansion in volume Initial volume × Temperature rise  R P Q Real increase in volume Initial volume × temperature rise   r = a + Vessel Change in volume of liquid w.r.t. vessel 5. Cooling (Tensile Stress) ΔV = V0 ( r  3 ) T Expansion in enclosed volume [  vessel ; L  liquid] Increase in height of liquid level in tube when bulb was initially completely filled. h= 6. apparent change in volume of liquid V0 (γ L  3 )T  area of tube A 0 (1+2 )T Anomalous expansion of water : In the range 0°C to 4°C warter contract on heating and expands on cooling. At 4°C  density is maximum Aquatic life is able to survive in very cold countries as the lake bottom remains unfrpzen at the temperature around 4°C. 7. Thermal expansion of gases : (a) Coefficient of volume expansion [PV = nRT at constant pressure (b) Coefficient of pressure expansion 8. 9. 10. 11. γV  V 1  V0 T T V T  ] V T P 1 γP   P0 T T VT Liquids usually expand more than solids because the intermolecular forces in liquids are weaker than in solids. Rubber contract on heating because in rubber as temperature increases, the amplitude of transverse vibrations increases more than the amplitude of longitudinal vibrations. Water expands both when heated or cooled from 4°C because volume of water at 4°C is minimum. In cold countries, water pipes sometimes burst, because water expands on freezing.