What determines whether an object is a net emitter or a net absorber of radiant energy?

Wood is a better insulator than glass. Yet fiberglass is commonly used as an insulator in wooden buildings. Explain.

Usually, the temperature of the object determines this. Heat radiated is proportional to temperature to the fourth power. So temperature rises (as it absorbs heat)until temperature is such that the heat radiated is equal to the heat absorbed.

Isn't there a lot of captured air in the fiberglass?

To determine whether an object is a net emitter or a net absorber of radiant energy, we need to consider its physical and chemical properties. Two important factors that influence this are the object's temperature and its surface properties.

1. Temperature: According to the laws of thermodynamics, objects at a higher temperature radiate more energy than objects at lower temperatures. So, an object that is hotter than its surroundings will typically be a net emitter of radiant energy. On the other hand, if an object is colder than its surroundings, it will tend to absorb more energy than it emits and will be a net absorber.

2. Surface Properties: The surface properties of an object also play a role in determining its ability to absorb or emit radiant energy. Objects with dark, rough, or opaque surfaces tend to absorb more energy, as they can effectively absorb and trap incoming radiation. In contrast, objects with light, smooth, or reflective surfaces tend to reflect or transmit more energy, making them better at emitting energy.

Regarding your second question about wooden buildings and fiberglass insulation, the choice of using fiberglass insulation in wooden structures is primarily based on its thermal insulating properties rather than its ability to emit or absorb radiant energy. While wood itself is a good insulator, fiberglass insulation can provide even better insulation by trapping air between its fibers. This trapped air acts as a barrier against heat transfer through conduction and convection, reducing the flow of heat in and out of the building. Therefore, fiberglass insulation is commonly used in wooden buildings to enhance their overall energy efficiency and thermal performance.