How To Demonstrate Convection with a Tea Bag and a Lighter

In this video, Paul Cook demonstrates how to perform a simple but captivating experiment as we explore the fascinating world of convection using just a tea bag and a lighter. Watch as we uncover the principles behind heat transfer and the movement of air in this simple yet mesmerising demonstration.

Convection is a heat transfer process that occurs when warmer, less dense fluids or gases rise and cooler, denser fluids or gases sink, creating a continuous circulation of heat. You can demonstrate convection using a tea bag and a lighter by performing a simple experiment involving the heating of air.

Typically, in a GCSE convection practical experiment, students might use items like tea bags, as mentioned earlier, or other materials like beakers of water and food coloring, to visually observe convection currents. The goal is to help students understand the basic principles of convection and its application in everyday situations, such as the circulation of air in a room or the movement of fluids in a heating system.

In this experiment, we begin by lighting the tea bag and observing the direction of the rising smoke. As the tea bag burns, you’ll witness a powerful example of convection in action.

You will need:

• • • Tea bag (unused, dry, emptied and opened up)
    • Heatproof mat
    • 0.5m ruler with splint attached
    • Matches or lighter
    • Safety glasses

Method:

1. 1. Set up a safe area: Choose a well-ventilated and safe area to perform the experiment, away from flammable materials and with adult supervision if necessary. Use a heat-resistant surface or a plate to place the tea bag on during the experiment.
   2. Prepare the tea bag: Remove the tea bag from its packaging and ensure it’s dry. You can use any type of tea bag, but an unused, unopened bag is best for this experiment.
   3. Light the tea bag: Hold the tea bag by the string or staple, keeping your fingers away from the burning end. Light the other end of the tea bag using a lighter or matches. It will start to burn.
   4. Observe and describe: As the tea bag burns, pay close attention to the direction of the smoke. You will notice that the smoke rises upwards. This rising motion of the smoke is a demonstration of convection. Here’s the explanation:
      • The flame heats the air directly above it.
      • As the air gets heated, it becomes less dense and starts to rise.
      • Cooler, denser air from the surrounding area moves in to replace the rising warm air.
      • This creates a continuous circulation of air, and the rising smoke particles are carried along with it, creating the appearance of smoke rising.
   5. Repeat and vary: You can repeat the experiment with different temperatures of air to observe how it affects convection. For example, you can try holding the tea bag closer to the cup or glass with cold water to demonstrate how the temperature difference influences convection currents.
   6. Safety precautions: Be cautious while working with fire. Keep a safe distance from flammable materials, and have a fire extinguisher or water nearby in case of emergencies. Extinguish the tea bag completely after the experiment.

All health and safety measures are the responsibility of the teacher doing the demonstration. A thorough risk assessment should be carried out and guidance procedures followed. It is suggested that you practice before demonstration in front of a class.

This simple experiment with a tea bag and a lighter illustrates the concept of convection, which is a fundamental process in the movement of heat in fluids and gases. It helps you understand how warm air rises and cooler air sinks, leading to the circulation of air currents in various natural phenomena.

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