The photograph shows a boy, outside at night, holding an electric lamp. As strange as it might seem at first, the light being emitted is actually sunlight, or more accurately, the lamp is emitting solar energy! To understand how this is possible, consider the following: |
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Frame A: Sunlight falls on the photovoltaic cells. About 10% of the energy is converted into electricity. The remainder is lost as heat or reflected away.
Frame B: Electrical energy is transferred by a wire from the photovoltaic cell to a battery. Energy is lost during the transfer due to the electrical resistance of the wire. This resistance causes energy to be lost as heat.
Frame C: A chemical battery (made up of a series of voltaic cells) is used to store the electrical energy. Here, once again, some of the tranferred energy is lost. The chemical process of charging the battery's cell generates heat which is radiated and conducted away into the surroundings. When the battery is discharged, that is, when the light is turned on, more heat is produced by the chemical reactions in the battery and so further energy loss occurs.
Frame D: When the lamp is switched on a current flows from the battery to the lamp. Electrical resistance in the wire generates heat and causes still more energy to be lost.
Frame E: The light bulb contains a tungsten filament which heats to incandescence when an electrical current passes through it. The major fraction of the energy is radiated away by the light bulb as invisible infrared light. Only a very small fraction of the energy which reaches the light bulb is actually converted into visible light. The energy of the emitted light is solar energy, from sunlight... in a sense it is sunlight.
This girl (and her dog) are both solar powered. To understand how this is possible, consider the following: |
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Frame F: Sunlight falling on green plants energizes a process called photosynthesis. The solar energy absorbed by the plants allows them to create compounds called carbohydrates which store solar energy in their molecular bonds.
Frame G: The plants are harvested and stored as animal feed for the winter.
Frame H: Cattle and dairy cows are given the stored crops as food. The animals use the food for growth, the production of milk, and for basic metabolic purposes such as breathing and (in the case of mammals) maintaining body warmth.
Frame I: Humans drink milk and eat dairy procucts, such as cheese and butter.
Frame J: When actvities are undertaken by humans, we combine oxygen with (digested) food to release metabolic and muscular energy for such things as running and maintaining body warmth.
