The relationship between temperature and infrared (IR) radiation comes from the fact that all objects emit electromagnetic radiation based on their temperature, and for most everyday temperatures, that radiation is mainly in the infrared range.
1. Blackbody Radiation Principle
- Any object above absolute zero (0 K or −273.15 °C) emits radiation.
- As temperature increases:
- The total energy emitted increases (hotter objects emit more IR energy).
- The peak wavelength shifts toward shorter wavelengths (toward visible light).
- This is described by Planck’s law, Wien’s displacement law, and the Stefan–Boltzmann law.
2. Key Relationships
- Stefan–Boltzmann Law:
The total energy emitted per unit area ∝ T4T^4.
→ A small temperature increase means a big increase in IR output. - Wien’s Displacement Law:
Peak wavelength = constantTemperature\frac{\text{constant}}{\text{Temperature}}.
→ At room temperature (~300 K), peak emission is around 10 μm (infrared).
→ As temperature rises (e.g., red-hot metal at ~1000 K), peak shifts toward visible red/orange.
3. Everyday Examples
- Human Body (~37 °C / 310 K) → Emits mainly mid-IR radiation (~9–10 μm).
- Earth’s Surface (~15 °C / 288 K) → Emits IR detected by satellites for climate studies.
- Hot Stove (~500 °C) → Emits both visible red light and strong IR.
4. Importance
- This relationship allows:
- Thermal imaging (detecting temperature differences via IR).
- Non-contact thermometers (measure temperature by emitted IR).
- Climate research (tracking Earth’s heat balance).