Light and reflection · Grade 7
When light hits a smooth, shiny surface like a mirror, it reflects in a predictable way: the angle of incidence equals the angle of reflection, both measured from the normal (a line at 90° to the mirror). Rough surfaces scatter light in all directions instead, which is why paper does not show your reflection.
Key facts
- Law of reflection: angle of incidence = angle of reflection.
- Angles are measured from the normal, not from the mirror surface.
- A plane mirror image is upright, the same size, laterally inverted and virtual – as far behind the mirror as the object is in front.
- Smooth surfaces give specular (regular) reflection; rough surfaces give diffuse reflection.
- Turning a mirror through θ turns the reflected ray through 2θ.
- Two mirrors at angle θ make 360 ÷ θ − 1 images.