Light & Reflection
Year 7 🌊 Waves & Optics Understand how light travels and the laws of reflection.
💡 How Light Travels
Light is a type of electromagnetic wave that travels in straight lines at incredible speed.
| ⚡ Property | 📏 Value |
|---|---|
| Speed in a vacuum | 3 × 10⁸ m/s (300,000 km/s!) |
| Speed in air | Slightly less, ≈ 3 × 10⁸ m/s |
| Speed in glass | About 2 × 10⁸ m/s (slower!) |
| Speed in water | About 2.25 × 10⁸ m/s |
Sunlight takes about 8 minutes to travel 150 million km from the Sun to Earth!
🪞 The Law of Reflection
When light bounces off a mirror, the angle it bounces equals the angle it came in at. Angles are always measured from the normal (a line at 90° to the mirror surface).
🪞 Law of Reflection
$$\text{Angle of incidence} = \text{Angle of reflection}$$
$$\theta_i = \theta_r$$| 📝 Term | 📖 Meaning |
|---|---|
| Normal | A line at 90° to the mirror surface |
| Angle of incidence (θᵢ) | Angle between incoming ray and normal |
| Angle of reflection (θᵣ) | Angle between reflected ray and normal |
🔦 Example: If a ray hits a mirror at 30° to the normal, it reflects at 30° to the normal.
👁️ Images in Plane Mirrors
A flat (plane) mirror forms an image with specific properties.
| 🖼️ Property | 📝 Description |
|---|---|
| Position | Same distance behind the mirror as object is in front |
| Size | Same size as the object |
| Orientation | Laterally inverted (left ↔ right swapped) |
| Type | Virtual — cannot be projected on a screen |
The word AMBULANCE is written backwards on ambulances so drivers can read it correctly in their rear-view mirrors!
Ready to test yourself? Click the Quiz tab above to answer questions on this topic!
🪞 Reflection Angle Calculator
The angle of incidence always equals the angle of reflection (measured from the normal).