[Leejohnston]

## The Speed of Light — What the Equation Actually Means

### 1. The Equation

c ≈ 3 × 10⁸ m/s

This is the speed of light in a vacuum.

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### 2. What Each Symbol Means

- c = speed of light
- m = metres
- s = seconds

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### 3. What the Equation Is Telling Us

Light is not just fast —
it is the **maximum speed at which information can travel**.

Nothing with mass can exceed this speed.

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### 4. Where It Comes From (Intuition)

Light speed emerges from:
- electric fields
- magnetic fields
- the structure of space itself

It is not “about light” — it’s about reality’s limits.

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### 5. Worked Example

**How far does light travel in 1 second?**

≈ 300,000 km

That’s:
- around Earth **7.5 times**
- Earth → Moon in ~1.3 seconds

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### 6. Real-World Applications

- GPS systems
- Space communication delays
- Relativity and time dilation
- Modern electronics

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### 7. Common Misconceptions

- Light always travels at c → false (slower in materials)
- Nothing can go fast → false (things go fast, just not faster than c)

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### Try It Yourself

How long does light take to reach:
- the Sun?
- Mars?
- the nearest star?