Thermocouple thermometer with galvanometer or mV meter
Platinum resistance thermometer (with Wheatstone bridge or ohmmeter)
Constant volume gas thermometer (optional)
Beakers of water at known temperatures (ice, room temp, boiling)
Place each thermometer type into a beaker of ice-water (0°C). Record each reading.
Transfer to a beaker of boiling water (100°C). Record each reading again.
Point out that each relies on a different physical property that changes with temperature: mercury-in-glass → length of liquid column; thermocouple → EMF between junctions; platinum resistance → electrical resistance; constant volume gas thermometer → pressure of gas.
Each thermometer responds to temperature change through a different physical property.
All read approximately the same temperature when immersed in the same medium.
The thermometric property used determines the type and accuracy of the thermometer.
Each thermometer is like a different translator for the same book — they all communicate 'temperature' but through different languages (length, voltage, resistance, pressure).
List 4 thermometric properties: length of liquid column, EMF of thermocouple, resistance of platinum wire, pressure of gas at constant volume. Know one advantage of each type.
2Different Thermometers Give Different Readings
Mercury-in-glass thermometer
Thermocouple thermometer
Resistance thermometer
Large beaker of water
Thermostatic water bath or Bunsen burner
Heat the water bath to approximately 60°C.
Immerse all three thermometers simultaneously in the same bath.
Read and record each thermometer's value when stable.
Note that none of the thermometers will agree exactly — they differ slightly because they are calibrated against different physical properties that do not all change identically with temperature.
The International Temperature Scale defines exact agreement points — but between them, thermometers based on different properties diverge slightly.
The three thermometers give slightly different readings at the same temperature.
This occurs because different thermometric properties (e.g. length of mercury column, resistance of platinum) do not change proportionally in the same way at all temperatures.
The differences are small but measurable.
It's like measuring a room's length using a steel ruler versus a wooden ruler on a hot day — the steel barely expands but the wood does, so they give slightly different readings.
Explanation: different thermometric properties do not change linearly in the same way. The thermodynamic temperature scale (Kelvin) provides a standard reference.
3How Different Solids Conduct Heat at Different Rates
Rods of equal length and diameter: copper, aluminium, iron, glass (or wood)
Petroleum jelly (Vaseline) and small identical metal balls or wax pellets
Bunsen burner
Retort stand and clamp
Ruler
Clamp each rod horizontally from one end. Attach small metal balls to the other end of each rod using small blobs of petroleum jelly as adhesive.
Apply the Bunsen burner flame simultaneously to the clamped end of all rods (same starting time and same heat source position).
Observe the order in which the wax melts (or the balls drop off each rod).
Record the time taken for the ball to drop off each rod.
The ball falls off the copper rod first, then aluminium, then iron, then glass/wood last (or not at all in the time of the experiment).
This demonstrates that metals conduct heat much faster than non-metals.
Conductivity order: copper > aluminium > iron >> glass/wood.
Think of how quickly a metal spoon in hot soup heats up compared to a wooden spoon — the metal conducts heat rapidly to your hand, the wood barely at all.
State: 'Heat is conducted through a solid by the transfer of kinetic energy from particle to particle without bulk movement of the material.' Metals are good conductors due to free electrons.
4Demonstration of Convection in a Liquid
Beaker of cold water
Potassium permanganate (KMnO₄) crystals
Bunsen burner and tripod
Dropping pipette or spatula
Ruler
Fill a large beaker with cold water. Allow it to settle.
Using a dropping pipette, carefully place one or two crystals of KMnO₄ at the bottom of the beaker — ideally directly above where the burner will be placed.
Gently apply heat with the Bunsen burner directly below the crystal position.
Observe the coloured stream of water from the crystals.
A purple stream of water rises upward from the KMnO₄ crystals at the heated point.
At the top of the beaker the stream cools, sinks at the sides, and flows back along the bottom — creating a convection current.
The entire circulation pattern can be followed by the purple colour.
This demonstrates that heat transfer in liquids occurs by bulk movement of the fluid.
Exactly like a lava lamp — the heated liquid at the bottom becomes less dense and rises while cooler, denser liquid sinks. The KMnO₄ makes the flow visible.
Key phrase: 'Hot liquid is less dense and rises; cooler liquid is more dense and sinks, setting up a convection current.' Convection requires fluid (liquid or gas) — it cannot occur in solids.
5Demonstration of Convection in a Gas
Wooden or cardboard box with two glass chimneys inserted through the top (about 30 cm apart)
Lighted candle
Smouldering taper or incense stick (to produce visible smoke)
Optional: glass front panel to view inside
Set up the box with two chimneys. Light the candle and place it directly below one chimney (Chimney B).
Allow time for a temperature difference to establish.
Hold the smouldering taper above Chimney A (the one without the candle) and observe the smoke movement.
The smoke provides visible evidence of the convection current direction.
Smoke from the taper held above Chimney A is drawn down and into the box.
Hot air (heated by the candle) rises up and out through Chimney B.
This creates a convection current: cool air enters through Chimney A, is heated by the candle, and exits through Chimney B.
This demonstrates convection in a gas.
This is exactly how old mine ventilation systems worked — a furnace at one shaft drew fresh air in from another shaft, circulating air through the mine by convection.
State: 'Hot air above the candle expands, becomes less dense and rises up Chimney B. Cooler, denser air flows in through Chimney A to replace it, setting up a convection current.'
6Demonstration of Heat Transfer by Radiation
Leslie's cube (a hollow metal cube with 4 different faces: shiny silver, dull black, dull white, shiny white/polished metal)
Thermopile connected to a galvanometer
Boiling water or very hot water
Metre rule
Fill the Leslie's cube with boiling water. Set it on a heat-proof mat.
Place the thermopile at a fixed distance (e.g. 20 cm) from each face in turn — ensuring same distance each time.
Record the galvanometer deflection for each face: shiny silver, polished, dull white, dull black.
The galvanometer reading indicates the intensity of thermal radiation detected.
The dull black surface gives the highest galvanometer reading — it radiates most heat.
The shiny silver surface gives the lowest reading — it radiates least heat.
Order of emission: dull black > dull white > polished/shiny silver.
This demonstrates that dark, rough surfaces are the best emitters of thermal radiation.
Black tarmac on a sunny day gets far hotter than a white-painted road surface because it absorbs (and also emits) radiation better — same principle as the Leslie cube.
Must state: 'Heat radiation is electromagnetic (infrared) waves and requires no medium.' Good absorbers are good emitters. Black body = perfect absorber and emitter. No medium needed.