- Review the following scene: REFLECTION

 is the change in direction of a light ray when it bounces off a surface For an observer standing beside the lake: 1. How are they able to see the mountains and the trees? 2. How are they able to see the reflection of the sky, mountains and trees in the lake? 3. Why is the reflection from the surface of the water such a clear image? - the sunlight reflects off every object in the scene and then enters their eyes - the sunlight reflects off every object in the scene toward the water and then is reflected from the surface of the water to their eyes REFLECTION - the water is so still that it acts like a mirror

Recall: Light travels in a straight line (as long as it is travelling through the same medium) medium: the substance through which light travels ray: a straight line with an arrowhead that shows the direction in which light waves are travelling Used in ray diagrams. (See page 413 – for an example and the steps involved.) REFLECTION

plane mirror angle of incidence ( i ) angle of reflection ( r ) Incident ray Reflected ray normal Law of reflection: angle of incidence = angle of reflection i = r “point of incidence” Reflection of Light (a typical ray diagram) (The ray of light coming from the light source toward a surface) (The ray of light that starts at the point of incidence) (A line that is perpendicular to the surface where a ray of light meets the surface)

Note: The incident ray, the normal, and the reflected ray all lie on the same flat surface, or plane.

Reflection Law Example = = = 55 Sample Problem: What is Ѳ ? 65° 25° 35° 55° Ѳ=55°

Specular vs Diffuse Reflection

diffuse reflection : reflection off of rough surfaces such as clothing, paper, and the asphalt roadway Note: Rough surfaces consist of a large number of different specularly-reflecting planes. specular reflection : r eflection off of smooth surfaces such as mirrors or a calm body of water

Specular reflection Diffuse reflection i i i r r r angle of incidence = angle of reflection in each case

A mirror with a flat, reflective surface. Plane Mirrors

light source eye Light entering the eye seems to converge (or “focus”) at the source. Light from the source is emitted (or reflected) in all directions. Only these rays (and the ones in between) enter the eye. How We See Things

Virtual Images in Plane Mirrors Draw the pen’s virtual image on the other side of the mirror in the position that you think it will appear.

Virtual Images in Plane Mirrors

How Do We See an Image in a Plane Mirror?

Why and How Do We See an Image in a Plane Mirror? Refer to page 414, figure The brain assumes that a light ray travels in a straight line. Therefore to find out where the eye “sees” the image, extend the rays that reach the eye backward until they meet at a point behind the mirror.

Same distance!

Plane Mirror Geometry Light from the castle appears to be coming from a point behind the mirror

Virtual Images in Plane Mirrors If light energy doesn't actually flow from the image, the image is "virtual". Rays seem to come from behind the mirror, but, of course, they don't. It is virtually as if the rays were coming from behind the mirror. "Virtually": the same; as if As far as the eye-brain system is concerned, the effect is the same as would occur if the mirror were absent and the chess piece (castle) were actually located at the spot labelled "virtual image". The image just LOOKS like it is behind the mirror. It is not REALLY there. If it was REALLY there, it would be a REAL image.

Ray Diagrams & Mirrors In general, an image has four characteristics: 1. Location (closer than, farther than, or the same distance as the object from the mirror) 2. Orientation (upright or inverted) 3. Size (same size, larger than, or smaller than the object) 4. Type (real image or virtual image) “LOST”

Images in Plane Mirrors An image in a plane mirror is the same distance from the mirror as the object 2. the same orientation as the object 3. the same size as the object. 4. a virtual image An image formed by rays that appear to be coming from a certain position, but are not actually coming from this position. The image does not form a visible projection on a screen Remember “LOST”

Homework Page 414 # 1 – 3 Page 418 # 1 – 8