Reflection of Light (by Plane Mirror)
1. Definition of Reflection of Light:
When light rays fall on a surface and bounce back into the same medium, the phenomenon is called reflection of light.
2. Terms Related to Reflection:
- Incident Ray: Ray striking the mirror.
- Reflected Ray: Ray bouncing off the mirror.
- Normal: Line perpendicular to the mirror at the point of incidence.
- Angle of Incidence (∠i): Angle between incident ray and normal.
- Angle of Reflection (∠r): Angle between reflected ray and normal.
3. Types of Reflection:
- Regular Reflection: From a smooth, polished surface like a mirror.
- Diffuse Reflection: From a rough surface; light scatters in many directions.
4. Laws of Reflection:
(i) The angle of incidence equals the angle of reflection (∠i = ∠r).
(ii) The incident ray, reflected ray, and the normal lie in the same plane.
5. Nature of Image Formed by Plane Mirror:
- Virtual and erect
- Same size as the object
- Laterally inverted
- Appears as far behind the mirror as the object is in front of it
6. Images in a Pair of Mirrors:
- Number of images = (360°/θ) − 1 (if 360°/θ is even).
- For mirrors at 90°, 3 images are formed; at 60°, 5 images; at 45°, 7 images.
- If object is placed asymmetrically, one less image may appear.
7. Uses of Plane Mirrors:
- In dressing mirrors
- In periscopes
- In kaleidoscopes
- For decoration and optical instruments
- To make rooms appear brighter and larger
