Reflection

"We believe a scientist because he can substantiate his remarks, not because he is eloquent and forcible in his enunciation. In fact we distrust him when he seems to be influencing us by his manner"
I. A Richards

Edouard Manet - A bar at the Folies_Bergere
Spot the deliberate(?) mistakes

A general description of the reflection of electromagnetic waves is obtained by considering the wave nature of the radiation. However, when the wavelength of the radiation is small compared to any apertures or obstacles nearby we may treat the wave as a stream of "particles" traveling in a straight line. This is the situation when considering the formation of images by visible light in mirrors and lenses. In this case the straight lines in which the visible light waves travel are known as light rays . The study of the behaviour of light under these conditons is known as Geometric Optics.

Light rays undergo one of two types of reflection - diffuse or specular.
- Diffuse reflection is more common for almost all objects. The reflected light is emitted in all directions due to irregularities on the surface of the material.
- Specular reflection occurs if the irregularities of the surface are small compared to the wavelength of the light. In this case reflection occurs at a single angle, for example from the surface of a plane mirror or water.
We will consider only specular reflection in this course

The law of reflection.(which can be derived from Maxwell's equations)

Angle of incidence = angle of reflection

Angles are measured with respect to the normal to the surface.

Ray Tracing and Image Formation in a plane mirror

Light rays are reflected from a plane mirror according to the law of reflection. An image is formed on the "other" side of the mirror, where the reflected rays appear to originate.

Images formed in plane mirrors have the following properties,
- Located the same distance behind the mirror as the object is in front of the mirror.
- Same size as the object.
- Right and left inversion
- Upright
- Virtual
An image is virtual if light rays do not physically pass through it. Real images are formed if light rays actually pass through the image.

"The tides are a fight between the Earth and Moon. All water tends towards the moon, because there is no water in the moon, and nature abhors a vacuum. I forget where the sun joins in this fight."
Middle School Science Test Answer

Dr. C. L. Davis
Physics Department
University of Louisville
email: c.l.davis@louisville.edu