Net rate of heat transfer by radiation

Definition

Net rate of heat transfer by radiation is the amount of thermal energy exchanged between objects due to electromagnetic radiation per unit time. It depends on the temperature and emissivity of the objects involved.

5 Must Know Facts For Your Next Test

1. The net rate of heat transfer by radiation follows the Stefan-Boltzmann Law, which states that the power radiated per unit area is proportional to the fourth power of the temperature: $P = \sigma A e T^4$.
2. Emissivity (e) is a measure of an object's ability to emit infrared radiation and ranges from 0 (perfect reflector) to 1 (perfect emitter).
3. The net heat transfer between two objects also depends on their relative temperatures and can be calculated using $Q_{\text{net}} = \sigma A e (T_1^4 - T_2^4)$.
4. Radiative heat transfer does not require a medium; it can occur in a vacuum, unlike conduction or convection.
5. Objects with higher surface areas and higher temperatures will radiate more energy.

Review Questions

• What law describes the relationship between an object's temperature and its radiative power?
• How does emissivity affect the net rate of heat transfer by radiation?
• Can radiative heat transfer occur in a vacuum? Why or why not?

Related terms

Stefan-Boltzmann Constant: $\sigma$ is a physical constant used in the Stefan-Boltzmann Law, approximately equal to $5.67 \times 10^{-8} \text{W m}^{-2} \text{K}^{-4}$.

Emissivity: A dimensionless quantity representing how effectively a surface emits thermal radiation compared to a perfect blackbody.

Blackbody Radiation: The theoretical spectrum of electromagnetic radiation emitted by an idealized object that absorbs all incident radiation, regardless of frequency or angle.