[Leejohnston]

## 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?