Objectives – Students will be able to:1) Identify the incident and reflected angle2) Explain why mirrors need to be smooth in order to work well.3) Draw the location of the virtual image produced by a mirror.

Reflection and MirrorsCh. 29 in your text book

Reflection

Incident rayReflected ray

Incident ray – the ray of light approaching the material

Reflected ray – the ray of light leaving the material

The normal line is always placed where the incident ray hits the material surface.

Reflection

Incident angle – the angle between the normal and the incident ray of light

Reflected angle – the angle between the normal and the reflected ray of light

θIncident ray

Incident angle

θReflected ray

Reflected angle

Reflection

Use your hands to show me a line that is normal to the following lines?

Reflection Lab

The reflected angle and incident angle will always be the same. These angles are measured with respect to the normal line.

Reflection

30° θReflected ray

Reflected angle

60°How large is the incident angle?

The reflected angle and incident angle will always be the same. These angles are measured with respect to the normal line.

Reflection

How large is the incident angle?50°

40°

The reflected angle and incident angle will always be the same. These angles are measured with respect to the normal line.

Reflection

25°

How large is the incident angle?

65°

MirrorsWe see the light that enters our eye. Mirrors need to be smooth in order to reflect light well. No surface is perfectly smooth, but the smaller the bumps are, the smoother the surface is.

MirrorsWhen we polish something, all we’re doing is making smaller bumps on the surface.

MirrorsSmooth surfaces reflect more light in the same direction.

Rough surfaces reflect light in many directions.

MirrorsA mirror is often glass with a reflective surface on one side.

glass

Reflective surface

All mirrors create images, either real or virtual

side view of a mirror

Flat Mirrors

Virtual image – An image created by the illusion that light is coming from an object or passing through it. Light does not come from a virtual image. Most mirrors produce this kind of image.

4m

8m

4m

Flat MirrorsThe image in a flat mirror is as far from the mirror as the object is.

Check for understanding: If you are doing your makeup one foot away from the mirror, how far away from you is the image of yourself that you’re looking at?

Check for understanding: With your partner, answer the following questions about the image below

How far from the man is the virtual image of himself?How far from the chair is the virtual image of itself?How far from the man is the virtual image of the chair?

Flat Mirrors

A ray diagram lets us see the path that an isolated ray of light travels. These diagrams help us figure out what we see when light is reflected.

Ray Diagrams For Mirrors

Light leaves the red dot, reflects off the mirror, and hits our eye. How do we draw that ray diagram? The normal line needs to be half way

between the object and your eye

Ray Diagrams For Mirrors

The incident and reflected rays will make the same angle to the normal. If the incident and reflected angles are different, it means the normal line isn’t half way between the object and the eye.

Where do we see image in the mirror?

We think we see it along the same line as the reflected ray that hits our eye.

Reflection

In your notes, draw how the light reflects from the mirror into our eyes and draw where the image is that we see in the mirror.

Reflection

This is not the reflected ray, but it still is at the same angle to the normal

Reflection

How would we draw the image of the box in the mirror?

Reflection

Not all mirrors are flat.

2) Start by draw a horizontal ray from each point to the mirror.

3) Draw normal lines

4) The reflected angle needs to be the same as the incident angle. The arrows will also need to be the same length.

1) Choose two points that aren’t next to each other

With your partner, come up with a couple examples of where we see these types of mirrors used.

Curved Mirrors

Concave mirror – rays converge to one location (focus)

Curved Mirrors

Curved mirrors follow the same rules as flat mirrors – the reflected angle is the same as the incident angle.

Reflections For Concave Mirrors

Convex mirror – rays diverge, spread out

Curved Mirrors

Reflections For Convex MirrorsCurved mirrors follow the same rules as flat mirrors – the reflected angle is the same as the incident angle.

U of A Mirror Lab

U of A Mirror Lab

U of A Mirror Lab

U of A Mirror Lab

These mirrors are very carefully, precisely polished. It doesn’t take much for them to completely miss what they’re trying to see. If the reflection is a small fraction of a degree off at the mirror, it will end up being sent way off the path we intended.

To Finish Up…On the small piece of paper, please do the following:1) Identify the incident angle in the diagram to the right.2) Explain why mirrors need to be smooth in order to work

well.3) Draw the location of the virtual image of the Dorado

head (don’t worry about too much detail)

flat mirror

ABC

D

Snell’s lawLight goes from small n to larger n – angle moves toward normalLight goes from larger n to small n – angle moves away from normalCheck for understanding on angle moving to or from normalLarger n = slower speed of lightCheck for understanding – Rank the following n for how fast light travels, rank fastest to slowestShow light going through 5 different materials –rank indices of refraction from biggest to smallest; rank speed of light from fastest to slowestExamples of calculations, specifically how to get the angle