The Colour of Solar Energy

Before you begin

• Use the safety checklist to help you plan and risk assess your activity. There's also more guidance to help you carry out your risk assessment, including examples.
• Make sure all young people and adults involved in the activity know how to take part safely.
• Make sure you’ll have enough adult helpers. You may need some parents and carers to help.

Planning and setting up this activity

• Always stay sun safe by using sunscreen, wearing hats and sunglasses, staying hydrated, and having lots of rest breaks in the shade or indoors. Use NHS sun safety guidance and our hot weather guidance.
• Make sure to use child-safe, waterproof digital thermometers in this experiment.

Running this activity

1. Gather everyone together and explain you’ll be doing a science experiment to learn about radiation.
2. Ask if anyone knows what radiation is. Radiation is energy that travels from one place to another, often in the form of waves. There are different types of radiation, including light, sound, heat, and X-rays. The sun produces a lot of energy, and this energy travels to us as both visible light and infrared radiation (heat). Visible light has shorter wavelengths than infrared radiation, which is why we can see colours but not infrared light. The visible light is made up of a range of colours, each with different wavelengths. For example, red light has longer wavelengths, while blue light has shorter wavelengths. The infrared radiation from the sun also reaches us, and it’s what we feel as heat. When you stand in the sunlight, you feel warm because your body’s absorbing this infrared radiation. If a cloud blocks the sun, you absorb less infrared radiation and feel cooler.
3. Explain that you’re going to use four bottles of water and test how the temperature of the water changes when the bottles are different colours. Ask everyone how they think an object’s colour might impact how good it is at absorbing or emitting heat. You can let a few people share their answers if they’d like to.
4. Everyone should get into small groups. Each group should take four bottles and fill each one with the same amount water.
5. Each group should wrap coloured paper or card around their bottles, then secure it in place with masking tape. One bottles should be wrapped in black paper, one bottle in white paper and the other two bottles can be any two different colours.
6. When they’ve wrapped the bottles, someone in each group should measure and write down the ‘before’ temperature of the water in each bottle. Remember to write down the bottle’s colour next to its result.
7. Ask everyone to guess which bottle they think will get the hottest when it’s placed in direct sunlight. They could circle or write down their guess. They could also write down how much they think the water’s temperature will increase or decrease by.
8. Next, place all the bottles close to each other in direct sunlight, making sure that each groups bottles are placed in the same area. All four bottles need to be exposed to the same amount of sunlight.
9. Next, set a time for 20 minutes. You could use this time to tidy up or to play a game.
10. After 20 minutes has passed, each group should go their bottles and use a digital thermometer to measure the water temperature in each bottle again. The results should be written down next to the ‘before’ temperatures.
11. When you’ve got the results, move the bottles inside (or into a shaded area) and allow them t cool down.
12. Gather everyone back together and ask them what their results show. Did anyone guess correctly as to which bottle got the hottest? The water in the bottles wrapped in darker colours, especially black, should have become hotter than the water in the lighter coloured bottles.
13. You could see if there’s any other factors that might have impacted the water’s temperature, such as:
    • Sunlight: If the bottles are in a sunny spot, they’ll get warmer because they absorb more heat from the sun. In shaded areas, they stay cooler.
    • Surface: Dark surfaces, such as grey tarmac, get hotter than light-coloured surfaces. So, bottles on dark surfaces might have warmer water.
    • Air Temperature: Places with warmer air will make the water in the bottles warmer too.
    • Wind: Windy areas can cool down the bottles faster, while sheltered spots keep them warmer.
14. Explain that different colours handle the sun’s energy differently. Dark colours, such as black, absorbs most of the sun’s energy, absorbing more light and Infrared radiation. This absorbed energy is converted into heat, which makes dark-coloured objects warmer. However, light colours, such as white, reflect most of the sun’s energy, absorbing less light and Infrared radiation. Because lighter-coloured objects absorb less light and heat, light-coloured objects stay cooler.
15. After the bottles and water have cooled, remove the masking tape and paper, then recycle the paper. You can use the water-to-water plants and recycle the bottle.