Flashlight Battery Energy - Light and Heat

Diagram 1.

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Phenomenon:

Students notice that a flashlight is very bright when the batteries are fresh. After using it for a while, the light becomes dimmer, and the flashlight body feels slightly warm. Students wonder: Where does the energy from the batteries go, and how can we show that energy is conserved when it is transferred and converted?

A flashlight is a good example of how energy can be transferred and converted without being created or destroyed. Inside the flashlight, the batteries store chemical energy. When the switch is turned on, this chemical energy is transferred into electrical energy that flows through the wires. The electrical energy is then converted into two new forms: light energy from the bulb and heat energy from both the bulb and the flashlights casing.

As the batteries lose chemical energy, the flashlight becomes dimmer because there is less energy available to convert into light. However, the energy has not disappeared. Some of it becomes heat, which is why the flashlight can feel warm after being on for a while. The total amount of energy is still conserved; it has simply changed form.

Students can observe this by measuring how bright the flashlight is at different battery levels and how warm it becomes after shining for the same amount of time. These measurements help show that chemical energy is transferred and converted into light and heat energy, demonstrating energy conservation.

Table 1.

Graph of Information - Figure 1.

Graph of Information - Figure 2.