top of page

2.6 Required Practical: Thermal Insulators

GCSE Physics · AQA · Chapter 2: Energy Transfer by Heating

A free GCSE Physics lesson for AQA (8463) from OBA School: investigating how well different materials, and different thicknesses of one material, insulate a beaker of hot water. Watch the video, read the explanation and worked examples, then try the revision questions. You can work through the full lesson, with every video, practice quizzes and printable worksheets with mark schemes, in our free online course.

What you will learn

  • Describe a method to compare different materials, and different thicknesses of one material, as thermal insulators
  • Identify the independent, dependent and control variables and the hazards
  • Plot and interpret cooling curves and calculate temperature drops and rates of cooling
  • Evaluate the method, including resolution, repeatability and sources of error, and suggest improvements

Key words

  • Independent variable: The variable you change: the type of material (part 1) or the number of layers (part 2).
  • Dependent variable: The variable you measure: the temperature of the water, recorded at regular intervals.
  • Control variable: A variable kept the same so the test is fair, e.g. volume and starting temperature of the water.
  • Cooling curve: A graph of temperature against time. The steeper it is, the faster the water is cooling.
  • Resolution: The smallest change an instrument can show, e.g. 1 °C for a glass thermometer, 0.1 °C for a digital probe.
  • Repeatable: Results are repeatable if the same person using the same method gets similar results when they repeat it.

Aim and apparatus

Aim: to find out (1) which material is the best thermal insulator and (2) how the thickness of a layer of insulating material affects the rate of cooling.

Apparatus: kettle, small beaker (e.g. 150 cm³) and a larger beaker, measuring cylinder, thermometer (or temperature probe and data logger), stopclock, cardboard lid with a hole, and samples of materials such as newspaper, bubble wrap, cotton wool, felt or polystyrene beads.

Method

Part 1 – different materials

1. Place the small beaker inside the large beaker and pack the gap with the first material.

2. Use the measuring cylinder to pour the same volume (e.g. 100 cm³) of hot water from the kettle into the small beaker.

3. Put on the lid with the thermometer through the hole. Record the starting temperature and start the stopclock.

4. Record the temperature every 2 minutes for 20 minutes.

5. Repeat with each material, and with no material at all (a control to compare against), using the same starting temperature each time.

Part 2 – different thicknesses

6. Wrap the small beaker in 1, 2, 3, 4 … layers of the same material (e.g. felt), with the same lid, and repeat steps 2–4 for each number of layers.

Exam tip: Start each run at the same temperature, e.g. let the water cool to 80 °C before you start the clock. Rate of cooling depends on the temperature difference with the room.

Variables and hazards

  • Independent; Part 1 (materials) type of material; Part 2 (thickness) number of layers (thickness)
  • Dependent; Part 1 (materials) temperature of the water at regular intervals (or the drop in 10 minutes); Part 2 (thickness) the same
  • Control; Part 1 (materials) volume of water; starting temperature; same beakers and lid; thickness of each material; room temperature; time interval; Part 2 (thickness) volume; starting temperature; same material; same beakers and lid; room temperature
  • hot water / kettle; Risk scalding; Control measure fill the kettle only part-way, pour carefully, stand up and keep the beakers on a stable bench; cool any scald under cold running water
  • glass thermometer or beaker; Risk cuts if broken; Control measure do not use the thermometer to stir; place it where it cannot roll; report breakages

Results and analysis

Plot a cooling curve (temperature on the y-axis, time on the x-axis) for each material on the same axes. The best insulator gives the least steep curve and the smallest temperature drop.

Worked example: temperature drop and rate of cooling

Bubble wrap (graph above): 80.0 °C at the start, 71.1 °C after 10 minutes.
temperature drop = 80.0 − 71.1 = 8.9 °C
average rate of cooling = 8.9 ÷ 10 = 0.89 °C per minute

Answer: 8.9 °C; about 0.9 °C per minute

The curves get less steep over time because the rate of energy transfer depends on the temperature difference between the water and the room: as the water cools, the difference gets smaller.

Evaluation and improvements

  • Starting temperature not the same – hotter water cools faster, which is not a fair test. Wait until each sample is at the same starting temperature.
  • Reading the thermometer – read at eye level to avoid parallax error; a thermometer with 1 °C resolution limits the precision of small drops.
  • Improvement – use a temperature probe and data logger (resolution 0.1 °C) that records automatically at exact times.
  • Repeatability – repeat each test and calculate a mean temperature drop; identify and ignore anomalous results.
  • Energy loss from the top – always use the same lid, or the same material on top, so that energy loss through the top is the same each time.

Exam tip: Evaluate with specifics: name the error, say how it affected the results, then give a practical improvement.

Common mistakes

  • Calling the best insulator the one with the highest rate of cooling. The best insulator has the smallest temperature drop.
  • Listing “the temperature” as a control variable without saying which one: it is the starting temperature of the water.
  • Forgetting a control run with no insulation.
  • Saying a data logger makes results “more accurate” without explaining why: higher resolution and readings taken at exact times.

Revision questions

Try these, then check your answers below each one.

Question 1. A student wraps identical beakers of hot water in different materials. What is the dependent variable? (Choose from: the temperature of the water over time, the type of material, the volume of water, the starting temperature.)

Answer: the temperature of the water over time

Working: The student measures the water temperature at regular intervals (or the drop in a fixed time).

Question 2. Water in an insulated beaker cools from 82.0 °C to 69.5 °C in 10 minutes. Calculate the temperature drop.

Answer: 12.5 °C

Working: 82.0 − 69.5 = 12.5 °C.

Question 3. True or false? A temperature probe with a resolution of 0.1 °C can show smaller changes than a thermometer with a resolution of 1 °C.

Answer: True

Working: True. A higher resolution (0.1 °C) shows smaller changes, so readings are more precise.

Related lessons

Continue in the full course

This lesson is section 2.6 (AGCPH0206) of our free GCSE Physics course for AQA. In the full course you get every video for this section, a self-marking practice quiz, a printable worksheet with a mark scheme, chapter tests, and your progress saved. Go to the full GCSE Physics course.

 

 

 

 

 

 

 

bottom of page