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Battery energy is a key concept when understanding how devices like flashlights, or in this case, a 100 W lamp can operate over time using stored energy. Each battery has a certain energy capacity, measured in watt-hours (Wh). In our example, a standard flashlight battery provides 2.0 Wh of energy. This means that the battery can deliver one watt of power for two hours or two watts of power for one hour before it is fully discharged. Understanding this concept is crucial because it helps us estimate how many batteries we would need for a certain amount of energy requirement. To paint a clear picture, if you want to power a device that needs 100 watts for 8 hours, you'll need a total of 800 watt-hours (100 W times 8 hours). Knowing the energy capacity of each battery allows you to figure out how many batteries are required to meet this energy need. This forms the basis of calculating costs when using batteries for power.

Power consumption refers to the amount of energy a device uses over a certain period. It is measured in watts (W). If we know a device's power consumption, we can calculate the total energy it will use over time. In this scenario, the lamp uses 100 W of power. To find out how much energy it consumes, multiply the power by the number of hours it is used. For example, using a 100 W bulb for 8 hours consumes 800 Wh of energy. Understanding this helps analyze how many batteries or what kind of utility rate is needed to cover this power demand. Furthermore, knowing the power consumption can help you estimate costs beforehand, whether you are using batteries or paying for electricity from a utility provider.

The kilowatthour (kWh) is a unit of energy that equates to one kilowatt (1,000 watts) of power used for one hour. It is a common unit used by utility companies to measure energy consumption and calculate billing costs.To determine the cost of energy consumption using electric utilities, you typically multiply the energy usage in kWh by the cost per kWh. In our exercise, the utility charges US$0.06 per kWh.So, if you use 0.8 kWh (as calculated earlier by converting 800 Wh to 0.8 kWh), you simply multiply this by the cost per kWh: \[ 0.8 \text{ kWh} \times 0.06 \text{ USD} = 0.048 \text{ USD} \]This provides an economical view of powering the lamp for 8 hours using grid electricity rather than batteries. This comparison highlights the importance of understanding kilowatthour costs for efficient energy budgeting.