Nature’s Treasures · Lesson 3 of 8
The Sun: Energy for Life and Work
“See how the Sun’s heat and light support daily tasks, plants, animals and useful devices.”
• Describe everyday uses of sunlight and solar heat. • Explain the Sun’s role in drying and water evaporation. • Trace an animal’s food energy back to plants and sunlight. • Distinguish solar panels, solar cookers and solar water heaters.
The familiar Sun as a source of energy
Ajji spreads chillies in sunlight so that they dry and can be stored for later. We also dry clothes or cut mangoes in the Sun. These familiar changes reveal that sunlight brings heat as well as light. The Sun is the main source of energy for life on Earth, even when the connection is indirect.
Heat, light and drying
Wet clothes or sliced fruit contain water. Warmth from the Sun helps that water evaporate into the air, leaving the material drier. The same solar heat contributes to evaporation of water in nature. Daylight makes it possible to see without artificial lighting during much of the day. Try drawing separate examples for uses of heat and uses of light, then decide where both are involved.
The change of liquid water into water vapour; warmth from the Sun can help it happen.
Problem
Fresh chillies are spread in a sunny place. Why will they become drier?
- 1.Sunlight warms the chillies and the water in them.
- 2.Some liquid water evaporates and moves into the surrounding air.
- 3.With less water remaining, the chillies are drier. Keep food clean and protected while drying it.
Plants connect sunlight with food
Green plants use sunlight to prepare their food. An animal may eat a plant; another animal or a person may eat food that came from a plant or animal. Consider a cow grazing grass. The cow receives food from the grass, and the grass needed sunlight to grow and make food. Thus sunlight is the original energy source in this simple food relationship, even though the cow is not obtaining food merely by standing in sunshine.
Problem
One child says a cow gains energy directly because it stands in the Sun. Another points to the grass it eats. Explain the fuller chain.
- 1.The cow eats grass, so the grass is its immediate food.
- 2.Grass is a plant and needs sunlight to prepare food.
- 3.The cow’s food energy can therefore be traced indirectly to the Sun. Standing in sunshine alone is not eating.
A cow can feel heat and light from the Sun, but it obtains food by eating. Trace the food pathway through plants when explaining the Sun’s role.
Putting solar energy to work
A solar panel captures energy from sunlight and produces electricity. Panels can be placed on rooftops, street lights or traffic signals. A solar cooker uses the Sun’s energy for cooking, while a solar water heater uses it to warm water. These devices have different outputs even though the Sun is their shared source.
| Device | Energy from the Sun is used for |
|---|---|
| Solar panel | Producing electricity |
| Solar cooker | Cooking food |
| Solar water heater | Heating water |
Problem
A building wants electricity for lights and separately wants warm water. Which solar devices suit each job?
- 1.A solar panel is used when the desired output is electricity.
- 2.A solar water heater is used when the desired output is heated water.
- 3.Both depend on receiving suitable sunlight, but they do different jobs.
Imagine several cloudy days when little direct sunlight is available. Daytime may be dimmer and solar devices may produce less energy, but the Sun has not vanished and stored energy or other sources may still be used. The cow’s body also does not instantly stop using food energy: its immediate source remains the grass it eats. This helps distinguish a direct need for current sunlight from an indirect energy pathway.
Quiz
Why do wet clothes dry more readily in sunshine?
Where does a cow get its immediate food in the chapter’s example?
How is the cow indirectly dependent on the Sun?
What is the output of a solar panel?
Which device is designed to warm water with solar energy?
Which statement best distinguishes a solar cooker from a panel?
Practice Problems
- Explain the drying of wet clothes or chillies using evaporation.
- Draw a path from Sun to grass to cow and label what is transferred at each step.
- Explain why standing in sunlight does not by itself feed a cow.
- Match solar panel, cooker and water heater to three different needs.
- List three activities that use sunlight or solar heat and explain each connection.
- Suppose sunlight is weak for several days. Predict one possible effect on a solar panel and distinguish it from the food already eaten by a cow.
Key Takeaways
• The Sun supplies heat and light and helps water evaporate during drying. • Plants use sunlight to make food; animals can depend on that food indirectly. • The cow eats grass, whose food-making depends on sunlight. • Solar panels produce electricity; solar cookers cook and solar water heaters warm water.