Optics Lesson 4Reflection In Curved Mirrors

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.

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)

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.

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

Concave Mirror Rules

Concave Mirror Rules

Concave Mirror Rules

Concave Mirror Rules

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

Ray Diagrams

F

Object beyond C

Object at C

Object between C and F

Object at F

Object between F and mirror

Properties of a Converging Mirror p. 499

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?)

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?

End of Day 1

Optics Lesson 4Reflection In Curved Mirrors

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)

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.

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

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

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

Convex Mirror Rules

Convex Mirror Rules

Convex Mirror Rules

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

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

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” ??????

One More DemonstrationConcave vs. Convex Curved Mirrors

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