optics lesson 4 reflection in curved mirrors. terminology centre of curvature (c) – middle of the...
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Optics Lesson 4Reflection In Curved Mirrors
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TerminologyCentre of curvature (C) – Middle of the
“circle” Focus (focal point) (F) – Where reflected
rays all intersectPrincipal Axis (PA) – The line drawn
through the centre of the mirror (and meeting the mirror at 90°)
Vertex (V) – The exact point where the PA meets the mirror.
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RecallLight rays always have an Angle of
Reflection = Angle of IncidenceThis equal angle is between the ray and the
normal with is a90° to the mirrors surface at the point where the ray hits the mirror
Angle of Incidence
Angle of Reflection
Normal (90° to mirror surface)
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TerminologyConcave Mirrors – are also known as
converging mirrors as the light converges at the focus in front of the mirror and creates a real image.Mirror is “caved” in
Convex Mirrors – are also known as diverging mirrors as the focus is found behind the mirror (virtual image) and is found by tracing back the reflected rays in a straight line.
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Focal Point – Concave Mirror
We can use parallel rays to PA to find the focal length of a concave mirror.
All parallel lines will reflect into the focal point
*note the normal is 90° to the point on the mirror where the ray strikes
The focal point for a concave mirror is to the left
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Concave Mirror Rules
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Concave Mirror Rules
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Concave Mirror Rules
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Concave Mirror Rules
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Ray Diagrams – Concave Mirrors
You need 2 rays to locate an image.The image is located where the rays intersect.If the rays do not intersect, you need to trace them
back to the point where they intersect.You need to include 2 basic rays.1. A parallel ray is reflected to the mirror then through
the “focal point”2. A ray is sent through the focal point is reflected
parallel to the principal axis.
F
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Ray Diagrams
F
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Object beyond C
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Object at C
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Object between C and F
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Object at F
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Object between F and mirror
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Properties of a Converging Mirror p. 499
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Uses of Concave MirrorsSearchlights, car headlights and flashlights all use concave mirrors to create
parallel or almost parallel beams of light (Why?)
Telescopes and satellite dishes use concaves mirrors to focus electromagnetic waves at the focal point (Why?)
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Uses of Concave Mirrors Con’t
We can also use concave mirrors to magnify a reflection close up. Why does it give this type of reflection?
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End of Day 1
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Optics Lesson 4Reflection In Curved Mirrors
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RecallLight rays always have an Angle of
Reflection = Angle of IncidenceThis equal angle is between the ray and the
normal with is a90° to the mirrors surface at the point where the ray hits the mirror
Angle of Incidence
Angle of Reflection
Normal (90° to mirror surface)
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TerminologyConcave Mirrors – are also known as
converging mirrors as the light converges at the focus in front of the mirror and creates a real image.Mirror is “caved” in
Convex Mirrors – are also known as diverging mirrors as the focus is found behind the mirror (virtual image) and is found by tracing back the reflected rays in a straight line.
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Focal Point – Convex MirrorThe focal point for
a convex mirror is to the right.
It can be found by drawing lines parallel to the PA towards the mirror
Extend the reflected lines past the mirror
Where the imaginary lines intercept is the focal point
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Centre of sphere – Convex Mirror
The C for a convex mirror is to the right.
It can be found by drawing a line perpendicular to the mirror at any point
Extend the reflected lines past the mirror
Where the imaginary lines intercept the PA is the C
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Convex Mirror RulesThe difference between a concave mirror
and a convex mirror is that in a convex mirror, F (now called a virtual focus) and C are behind the mirror and light rays seem to come from an apparent light source behind the mirror
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Convex Mirror Rules
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Convex Mirror Rules
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Convex Mirror Rules
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Ray Diagrams – Convex MirrorsThe image is located where the extended reflected lines
intersect behind the mirrorYou need to include 2 basic rays.1. A parallel ray that extends from the top of the
object to the mirror and is reflected back to the viewer
2. A ray is directed towards the focal point and is reflected parallel to the principal axis.
3. Extend the reflected rays past the mirror until they intersect
4. The point of intersection is the top of the image. The image extends down to the Principal axis
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Images in a Convex MirrorThe rays reflected off a convex mirror always diverge
Reflected rays from an object never cross in front of the mirror to form a real image
Instead it ALWAYS creates a smaller, upright, virtual image
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Uses of Convex MirrorsConvex mirrors show a wide range of view with their smaller virtual image
.
Used in:Security mirrors Side-view mirrors in cars“Objects in mirror are
closer than they appear” ??????
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One More DemonstrationConcave vs. Convex Curved Mirrors
http://www.phy.ntnu.edu.tw/ntnujava/index.php?PHPSESSID=643ae5051e223f1f696d419c040b986d&topic=48.msg297#msg297