# 18.2 Reflection and Mirrors

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18.2 Reflection and Mirrors
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Reflection of Light Rays
The reflection you see in the mirror depends on how the surface reflects the light Rays are straight lined representations of how light reflects Light rays obey the law of reflection The two ways in which a surface can reflect light are regular reflection and diffuse reflection

Regular Reflection When parallel rays of light hit a smooth surface, regular reflection occurs All the light rays reflect at the same angle Produces a sharp reflection

Diffuse Reflection When parallel rays of light hit a bumpy or uneven surface, diffuse reflections occur Light rays hit the surface at different angles because of the uneven surface Each light ray reflects at a different angle DO NOT see a clear reflection

Plane Mirrors Plane mirrors are a flat sheet of glass, that has a silver-colored coating on one side the coating reflects the light The coating is smooth = regular reflection occurs and a clear image forms Image is a copy of an object formed by reflected or refracted rays of light

What kind of image forms:
Virtual images are upright images that forms where light seems to come from Virtual = something that does not really exist Plane mirrors produce virtual images that are upright and the same size as the object Image not exactly same as object The left and right of the image are reversed

How Images Form Light rays from the object strike the mirror and reflect towards the observer’s eye Even though rays are reflected the observer’s brain treats them as if they had come from behind the mirror Image appears to be behind the mirror

Concave Mirrors A mirror with a surface that curves inward like the inside of a bowl is a concave mirror Reflects parallel rays of light so that they meet at a point The Optical Axis is an imaginary line that divides a mirror in half The Focal Point is the point at which rays parallel to the optical axis meet Depends on shape of mirror More curved the mirror the closer the focal point is to the mirror

Concave Mirrors The Optical Axis is an imaginary line that divides a mirror in half The Focal Point is the point at which rays parallel to the optical axis meet Depends on shape of mirror More curved the mirror the closer the focal point is to the mirror

X= Focal Point ---- = Optical Axis

Representing How Images Form
Ray diagrams are used to show where a focused image forms on a concave mirror Shows rays of light coming from points on the object Two rays coming from one point on the object meet or appear to meet at the corresponding point on the image ***Turn to pg. 620 to practice drawing ray diagrams***

Determining the Type of Image
Concave mirrors can form virtual or real images If an object is placed at the focal point = NO Image forms! if the light is placed at the focal point it can project parallel rays of light Ex. Car headlights

Real Vs. Virtual Images Real images form when rays actually meet
Occur if the object is farther away from the mirror than the focal point May by larger or small than the object Virtual images form when the object is between the mirror and focal point are always larger than the object for concave mirrors

Convex Mirrors Convex Mirrors are mirrors with surfaces that curve outwards rays spread out but appear to come to from a focal point behind the mirror Because rays never meet, images formed by convex mirrors are always virtual and smaller than the object Used in car mirrors Advantage: allows you to see a larger area than you can with a plane mirror Disadvantage: images appears further away than it really is