Transcript 18.2 Reflection and Mirrors

18.2 Reflection and Mirrors
Pg. 617-622
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