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Scientists agree that our planet is getting warmer. But is there a human cause for global warming, or is it a natural fluctuation in a long-term cycle? Warming cycles throughout Earth's history have caused glacial melting, animal and plant habitat shifts, and earlier flowering seasons for trees. These climate changes often correlate with changes in Earth's orbit known as Milankovitch cycles. For example, Earth's angle of axial tilt varies over the course of 41,000 years from 22.1° to 24.5%. At greater angles, Earth's poles receive more direct solar radiation, or insolation. Increased insolation results in higher mean temperatures. The Milankovitch theory proposes that cycles in climate arise from these cyclical changes in Earth's orbit. According to one viewpoint, the current warming of our planet is just evidence of a Milankovitch cycle. However, current climate changes are occurring at a faster rate than those in the To explain the different rates, many scientists point to human use of fossil fuels. Fossil fuels release carbon dioxide (CO,) when burned. CO, traps thermal radiation in Earth's atmosphere, a phenomenon known as the greenhouse effect. Recent increased levels of CO, correlate very strongly with increased mean temperatures. Furthermore, the rate of Increase in CO, levels is also rising. For this reason, many scientists conclude that climate change is anthropogenic (caused by humans). Data that support Milankovitch cycles do not necessarily contradict this conclusion. Supporters of the anthropogenic climate change model only need to demonstrate that the current warming deviates from Milankovitch cycles and that human activities provide a better explanation, Both the anthropogenic climate change model and the Milankovitch theory are consistent with some of the observed climate changes. However, only one offers the best explanation for the current warming of Earth.

A 60W light bulb used .48 kilowatt hours of electricity. How long was the light bulb on?

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Rationale

The light bulb was on for 8 hours.

Given that a 60W light bulb consumes power at a rate of 0.06 kilowatts, to find the duration it was on when it used 0.48 kilowatt hours, we divide the energy consumed by the power: 0.48 kWh / 0.06 kW = 8 hours. A) 0.48 hours is incorrect because this choice would imply the light bulb was on for only a fraction of an hour, which does not align with the energy consumed. The calculation shows that the bulb was on for 8 hours, not 0.48 hours, as this would only account for 28.8 watt-hours of energy. B) 28.8 hours is also incorrect. If the bulb was on for 28.8 hours, it would consume significantly more energy than 0.48 kilowatt hours. Specifically, 28.8 hours at 60W would use 1.728 kilowatt hours (28.8 hours × 0.06 kW), which far exceeds the given consumption. C) 0.125 hours is incorrect because this duration would result in a very low energy consumption of only 7.5 watt-hours (0.125 hours × 60W), which is much less than the 0.48 kilowatt hours stated in the question. This does not match the energy usage. D) 8 hours is the correct answer, as the calculations confirm that a 60W light bulb would consume 0.48 kilowatt hours after being operated for 8 hours (0.06 kW × 8 hours = 0.48 kWh). Conclusion To determine the duration a 60W light bulb was on based on its energy usage of 0.48 kilowatt hours, we calculate the time using the power formula. The bulb was indeed on for 8 hours, which aligns with the energy consumption, while the other choices incorrectly reflect either insufficient or excessive energy usage. This problem illustrates the importance of understanding power consumption and energy calculations in practical scenarios.

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