Both black and white road surfaces radiate energy. At midnight on a starry night the warmer road surface is the Oneither, as no noticeable difference. white surface. black surface?
The Correct Answer and Explanation is :
The correct answer is black surface.
The explanation lies in the concepts of absorption and radiation of energy. Both black and white surfaces absorb and radiate energy in the form of infrared radiation, but they do so differently due to their distinct physical properties, especially their albedo (reflectivity) and heat absorption characteristics.
- Absorption of Energy: Black surfaces have a low albedo, meaning they absorb most of the energy from sunlight or any surrounding heat sources. On the other hand, white surfaces have a high albedo, meaning they reflect most of the sunlight or surrounding heat, absorbing less.
- Heat Retention: Because black surfaces absorb more heat, they tend to get warmer when exposed to light, especially under the sun. In contrast, white surfaces reflect much of the incoming light, making them cooler during the day.
- Radiation at Night: At midnight, there is no direct sunlight, so the primary source of heat is the energy absorbed during the day. Both surfaces will radiate infrared energy (heat) according to the Stefan-Boltzmann law, which states that hotter objects emit more radiation than cooler ones. Since black surfaces absorb more heat during the day, they will be warmer than white surfaces at night. As a result, they will radiate more infrared energy compared to the white surface.
- Starry Night and Energy Radiation: In the absence of significant external heat sources like the sun, the black surface will remain warmer because it has absorbed more heat during the day. The white surface, being cooler, will radiate less energy. Therefore, on a starry night, the black surface will appear warmer because it is radiating more energy due to its higher temperature.
In conclusion, despite both surfaces radiating energy at the same time, the black surface will be warmer and radiate more energy due to its higher absorption of heat during the day.