1.4 Temperature and Thermal Expansion

• Temperature and its units
• Measurement of temperature: liquid expansion devices, bimetallic devices, thermocouples, resistive temperature devices, infrared radiators
• Thermal expansion: linear expansivity, unusual expansion of water
• Applications of thermal expansion

• explain the meaning of temperature as used in thermal physics
• measure temperature using different technologies
• investigate thermal expansion and contraction in solids and fluids
• describe applications of thermal expansion in solids and fluids
• appreciate the applications of thermal expansion in day-to-day life

“Why are gaps left between sections of a railway line?”

“Why does ice float on water when most solids sink in their own liquid?”

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1. Temperature and how we measure it
   40 min · 2 practice tasks · quiz
   What temperature actually is, why hot is not the same as a lot of heat, and the devices that put a number on it.
2. Thermal expansion and where it matters
   40 min · 2 practice tasks · quiz
   Why solids grow when heated, why railway lines have gaps, and the one liquid that breaks the rule.
3. How a liquid-in-glass thermometer works
   40 min · 1 practice tasks · quiz
   Bulb, capillary and scale: how a small expansion becomes a reading, and why a clinical thermometer is built differently from a laboratory one.
4. The Celsius and kelvin scales
   40 min · 1 practice tasks · quiz
   How the two scales are defined, why a change is the same number on both, and why physics prefers the kelvin.
5. Thermocouples, probes and infrared
   40 min · 1 practice tasks · quiz
   How a voltage, a changing resistance or a burst of infrared can stand in for a rising liquid thread.
6. Linear expansion and railway gaps
   40 min · 1 practice tasks · quiz
   Measure and calculate the extra length of a solid, then size the gap a Kenyan rail needs on a hot afternoon.
7. Area expansion of solids
   40 min · 1 practice tasks · quiz
   A sheet grows in two directions at once, so its area - and any hole in it - increases by about 2α A₀ ΔT.
8. Volume expansion and water tanks
   40 min · 1 practice tasks · quiz
   Solids and liquids grow in three directions; a brim-full school tank overflows because the water expands more than the tank.
9. Bimetallic strips and thermostats
   40 min · 1 practice tasks · quiz
   Two metals, one curve, and a contact that makes an iron, an oven or a fire alarm act at a set temperature.
10. Thermal expansion around Kenya
    40 min · 1 practice tasks · quiz
    Rails, KPLC lines, roof tanks and highland water: apply linear, area and volume expansion, and investigate why ice floats.