Physics / Unit 8: Light and Optics
8.2 Reflection and Plane Mirrors
Notes
Reflection is light bouncing off a surface.
- Law of reflection: the angle of incidence equals the angle of reflection. Both are measured from the normal, a line perpendicular to the surface.
- Specular reflection (smooth surface) makes clear images; diffuse reflection (rough surface) scatters light.
- A plane mirror makes a virtual, upright image the same size as the object, as far behind the mirror as the object is in front. The image is reversed left to right.
Practice
A light ray hits a mirror at $35^\circ$ from the normal. What is the angle of reflection?
The angle of reflection equals the angle of incidence, both measured from the normal.
You stand 2 m in front of a plane mirror. How far are you from your image?
The image is 2 m behind the mirror, so it is $2 + 2 = 4 \text{ m}$ from you.
Why can you see a clear image in a still pond but not in a sheet of paper?
Both reflect light, but rough surfaces scatter it in many directions.
Ready for more? Take the Unit 8 test.