Physical Science / Unit 9: Waves, Sound and Light
9.5 Reflection
Notes
Reflection is when a wave bounces off a surface.
- Law of reflection: the angle of incidence equals the angle of reflection, both measured from the normal (a line perpendicular to the surface).
- Smooth surfaces give regular (specular) reflection, like mirrors. Rough surfaces scatter light (diffuse reflection).
- A plane mirror makes an upright, same-size virtual image that appears as far behind the mirror as the object is in front.
- We see most objects because they reflect light into our eyes. A red shirt reflects red light and absorbs the others.
Practice
A ray hits a mirror with an angle of incidence of 35 degrees. What is the angle of reflection?
Angle of incidence equals the angle of reflection.
A person stands 2 m in front of a plane mirror. How far behind the mirror does the image appear?
The image is as far behind the mirror as the object is in front.
Why can you see your face in a mirror but not in a rough wall?
Diffuse reflection scatters rays; mirrors give regular reflection.
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