Core Practical: Investigating Thermal Energy

Section 1 of 7Experiment 1: conduction in different metals

1

Use a conduction ring with strips of iron, copper, brass and aluminium of equal length and width. Independent variable: type of metal. Dependent variable: time for the wax to melt.

2

Stick a ball bearing to the end of each strip with a small, equal blob of wax.

3

Turn the apparatus so the strips are upside down, supported on a clamp stand over a heatproof mat, and heat the centre where the strips meet gently with a Bunsen burner.

4

Start the stopwatch and record how long each ball bearing takes to fall as the wax melts.

5

Repeat the experiment and calculate a mean time for each metal.

Section 2 of 7Conduction: results and conclusion

Metal	Time for ball bearing to fall	Thermal conductivity
Copper	Shortest	Highest
Aluminium	Short	High
Brass	Longer	Lower
Iron	Longest	Lowest

Section 3 of 7Experiment 2: convection in water

1Set up

• Set up Half-fill a beaker with cold water on a tripod and gauze.
  • Use forceps to drop in a single potassium permanganate crystal at the side.

2Heat

• Heat Heat the beaker just below the crystal.
  • Water near the flame gains energy, expands and becomes less dense.

3Rise and fall

• Rise and fall The warm water carrying purple dye rises.
  • At the surface it cools, becomes denser and sinks, forming a convection current.

4Compare

• Compare Repeat with hot water (temperature is the independent variable).
  • Convection is faster because the molecules have more kinetic energy.

Section 4 of 7Experiment 3: radiation and surface colour

Method

• Method Fill four identical flasks, painted black, dull grey, white and shiny silver, with the same volume of hot water at the same starting temperature.
• Record the temperature of each flask every 30 seconds for 10 minutes.

Variables

• Variables Independent: surface colour. Dependent: temperature of the water at each time.
• Controlidentical flasks, equal volume and starting temperature of water, time intervals and room conditions.

Conclusion

• Conclusion All objects emit infrared radiation, and hotter objects emit more.
• The black flask cools fastest because dull, black surfaces are the best emitters and absorbers.
  • The shiny silver flask cools slowest because it is the worst emitter.

Section 5 of 7Safety and improving reliability

Thermal energy practicals

Burns

• Burns Bunsen burners, hot metal, hot water and the kettle can cause burns.
  • Tie back hair, handle hot items with care and cool any burn under cold running water.

Potassium permanganate

• Potassium permanganate Use forceps, not fingers, because the crystals stain skin and irritate it.
  • Wear eye protection.

Reliability

• Reliability Repeat each investigation and calculate means.
  • Use a data logger or digital thermometer for finer resolution than a 1 °C thermometer.

Section 6 of 7Key terms

Term	Meaning
Conduction	Transfer of thermal energy through a solid by vibrating particles and free electrons.
Convection	Transfer of thermal energy in liquids and gases by the movement of warmer, less dense fluid upwards.
Radiation	Transfer of thermal energy by infrared waves, which needs no medium.
Thermal conductivity	A measure of how well a material conducts thermal energy.
Emitter	A surface that gives out infrared radiation; dull black surfaces are the best.

Section 7 of 7Exam technique

1

Saying that heat 'rises'. Warmer, less dense fluid rises; thermal energy is transferred by that movement.

2

Forgetting to keep the flasks identical in the radiation test, so the result could be due to size or shape rather than colour.

3

Writing that a silver surface is the best absorber. Shiny surfaces are poor absorbers and poor emitters.

4

Using unequal amounts of wax in the conduction test, which makes the ball bearings fall at unfair times.