Investigating thermal radiation
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Explainer Video
Summary
Investigating thermal radiation
In a nutshell
By filling different coloured beakers with the same volume of hot water, the temperature of the beakers over time will be measured using a thermometer. This corresponds to the amount of thermal radiation radiated by the surface of the beaker.
Equipment list
The following equipment list can be used to conduct the experiment to investigate thermal radiation radiated by a surface.
Equipment | Use |
| Beaker (at least four) | To pour hot water into. |
| Different coloured materials | To clad each beaker with. These materials should be the same thickness and material. Colours should include white, silver, matte black and any other colours for the rest. |
| Thermometer (same amount as number of beakers) | To measure the temperature of the water. |
| Beaker lid with a hole for the thermometer (one for each beaker) | To allow the temperature of the water to be measured. |
| Kettle | To boil the water before putting it in the beakers. |
| Heatproof mat | To place the beaker on in order to prevent heat escaping from the bottom of the beaker. |
| Stopwatch | To time the experiment. |
Note: Alternatively, you can use four test tubes that are covered in different colour materials.
Experimental variables
The independent variable is the variable you change. The dependent variable is the variable that changes depending on the other variables, and is the one you measure. The control variables are the variables that are kept constant.
| Independent Variable | |
| Dependent Variable | |
| Control Variables | |
Safety precautions
When performing experiments, it is very important to consider safety precautions. This is so that no one gets hurt or injured during the experiment.
Hazard | Risk | Safety Measure |
| Hot water | The water will be near boiling temperature when it is poured into the beakers. This could cause burns if spilt on someone. | Don't rush when pouring the water. If burnt, run the burn under cold running water for five minutes. |
| Spilling water | The beakers may be knocked over whilst the water is still very hot. | Make sure the equipment is not at the edge of the desk. Perform the experiment whilst standing so you can react to spills quickly. |
| Beakers | If dropped, the beakers may smash and cause injury. | Handle the beakers with care and do not touch with hands when filled with hot water. |
Method
These are the instructions to complete the experiment. Record all measurements taken as you work through the experiment in a table.
 |
|
| 1. | Set up the apparatus as shown in the diagram. |
| 2. | Boil the kettle. Pour the same volume of water into each beaker and then cover each of them with a lid. Place the thermometer inside. |
| 3. | Measure the initial temperature of each beaker using the thermometer and start the stopwatch. |
| 4. | Measure the temperature of each beaker at regular time intervals until the beakers reach room temperature (around ). Make sure that you read the temperature straight on to avoid parallax error, as otherwise this would skew readings. Record the corresponding time on the stopwatch. Tip: Take a picture of all the beakers and read the temperature from that. This ensures they are all measured at the same time. |
Analysis
This is how you will use the data recorded to form conclusions.
| 1. | Plot a graph of temperature (-axis) against time (-axis). Draw a curved line to fit the data for each beaker and include a key. |
| 2. | Compare the gradient of the lines with the theory of thermal radiation. A matte black surface is the best at emitting radiation, so will radiate the most thermal radiation. This means it will cool down the fastest. Whereas a shiny material cools down slower, which is why the silver beaker should have cooled the slowest. The gradient shows the rate at which (how quickly) each of the beakers cool down. |
Conclusion
The graph from the measured values of the experiment should look similar to this. The black beaker cooled down the fastest, whilst the silver beaker was the slowest at cooling down. This should be seen in the graph with the black matte beaker reaching a lower temperature in the same time measured.
Evaluation
Once you have completed your experiment, it is important to consider how it could be improved. You should come up with ways to improve the accuracy of your values. If you got a result that seems unreasonable, think about why this was.
FAQs - Frequently Asked Questions
How do you measure the amount of radiation radiated by a surface?
By filling different coloured beakers with the same volume of hot water, the temperature of the beakers over time will be measured using a thermometer. This corresponds to the amount of thermal radiation radiated by the surface of the beaker.
What colour surfaces best radiate thermal radiation?
A matte black surface is the best at emitting radiation, so will radiate the most thermal radiation.
What is the independent variable in the thermal radiation experiment?
The independent variable is the colour of material that clads each beaker.