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Blackbody Radiation — Why Things Glow - Leejohnston - 01-08-2026
## Blackbody Radiation — Why Things Glow
### 1. The Equation
Stefan–Boltzmann Law:
P = σAT⁴
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### 2. What Each Symbol Means
- P = power radiated
- σ = Stefan–Boltzmann constant
- A = surface area
- T = temperature (kelvin)
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### 3. What the Equation Is Telling Us
Hot objects radiate energy.
A small increase in temperature causes a **huge increase in radiation**.
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### 4. Where It Comes From (Intuition)
Thermal motion of charged particles produces electromagnetic radiation.
Higher temperature → more violent motion → more radiation.
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### 5. Worked Example
If temperature doubles:
- radiated power increases **16×**
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### 6. Real-World Applications
- Stars
- Infrared cameras
- Climate science
- Astrophysics
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### 7. Common Misconceptions
- Only glowing objects radiate → false
- Radiation requires light → false
- Temperature scales linearly → false
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### Try It Yourself
Why do stars change colour as they heat up?