Reflection of Light from Plane Surfaces E. Alexander Burt Unit 9 Class 2

Smooth Surface Reflection When a ray of light hits a smooth, reflective surface such as a mirror its direction changes The angle of incidence  i is equal to the angle of reflection  r .

When a ray of light hits a smooth, reflective surface such as a mirror its direction changes

The angle of incidence  i is equal to the angle of reflection  r .

Smooth surface reflection 2 Notice that both angles are measured from a line perpendicular to the surface. This line is called a “normal” line – remember “normal force?” “Smooth” as it refers to mirrors means that variations in the surface are significantly smaller than the wavelength of light. Remember, visible light has wavelengths from 400 to 700 nm

Notice that both angles are measured from a line perpendicular to the surface. This line is called a “normal” line – remember “normal force?”

“Smooth” as it refers to mirrors means that variations in the surface are significantly smaller than the wavelength of light.

Remember, visible light has wavelengths from 400 to 700 nm

Rough Surface Reflection If the surface is not smooth enough (see previous slide) the light will reflect, but rays landing at different points will reflect at different angles.

If the surface is not smooth enough (see previous slide) the light will reflect, but rays landing at different points will reflect at different angles.

Terminology: Smooth surface reflection is called “specular” reflection. Rough surface reflection is called “diffuse” reflection. Examples: A mirror exhibits specular reflection A sheet of white paper exhibits diffuse reflection.

Smooth surface reflection is called “specular” reflection.

Rough surface reflection is called “diffuse” reflection.

Examples:

A mirror exhibits specular reflection

A sheet of white paper exhibits diffuse reflection.

Image Formation We can locate images by “ray tracing” – drawing the light rays on paper and reflecting them using a protractor and a ruler.

We can locate images by “ray tracing” – drawing the light rays on paper and reflecting them using a protractor and a ruler.

Ray Tracing, continued Notice in the diagram that all five rays are reflected according to the rule. The reflected rays are extended, using dotted lines, to the point where they cross behind the mirror.

Notice in the diagram that all five rays are reflected according to the rule.

The reflected rays are extended, using dotted lines, to the point where they cross behind the mirror.

Ray Tracing, part 3 The rays of light originate at point A The dotted extensions of the reflected rays cross at point A’ A’ is the location of the image of A By picking several points and following this process, we can find the reflected image of a larger object.

The rays of light originate at point A

The dotted extensions of the reflected rays cross at point A’

A’ is the location of the image of A

By picking several points and following this process, we can find the reflected image of a larger object.

Extended Object Ray Tracing Notice in the diagram below that many rays have been omitted to make it less confusing!

Notice in the diagram below that many rays have been omitted to make it less confusing!