This document provides information about ray diagrams and image formation using spherical mirrors. It discusses the key terms including principal axis, focus, center of curvature and explains how to use ray diagrams to determine the location, orientation, size and type of images formed by concave and convex mirrors in different configurations. Five cases of image formation using a concave mirror and one case using a convex mirror are described through diagrams and explanations of how the light rays behave. The document also includes examples for readers to practice locating and describing images.

1. J.M. Gabrielse
Ray Diagrams

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Spherical Mirrors
(concave & convex)

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Concave & Convex
(just a part of a sphere)
C: the centre of curvature (centre point of the sphere)
F: the focus (focus) of the mirror (halfway between C and the mirror)
•
C
•
F
Principal Axis
Curved Surface

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Principal axis
Concave Mirrors
(caved in)
•
F
Light rays that come in parallel to the principal axis reflect through the focus.
•
C

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principal axis
Concave Mirror Case #1
(image outside C)
•
F
•
C

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principal axis
Concave Mirror Case #1
(image outside C)
•
F
The first ray comes in parallel to the principal axis and reflects through the focus.
•
C

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principal axis
Concave Mirror Case #1
(image outside C)
•
F
The first ray comes in parallel to the principal axis and reflects through the focus.
The second ray comes through the focus and reflects parallel to the principal axis.
•
C

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principal axis
Concave Mirror Case #1
(image outside C)
•
F
The first ray comes in parallel to the principal axis and reflects through the focus.
The second ray comes through the focus and reflects parallel to the principal axis.
•
C

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principal axis
Concave Mirror Case #1
(image outside C)
•
F
A image forms where the light rays converge. When we describe the image formed, we
can use the acronym LOST (Location, Orientation, Size, Type).
This image is L - between F and C, O - inverted (upside down from original), S - smaller
than original and T - a real image (on the same side of the mirror).
•
C

10. J.M. Gabrielse
principal axis
Your Turn - Concave Case #2
(object at C)
•
F
object
concave mirror
• Locate and describe (LOST) the image of the arrow
•
C

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principal axis
Your Turn - Concave Case #2
(object at C)
•
Fobject
concave mirror
L - at C, O - inverted, S - same size, T - real
•
C

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principal axis
Concave Mirror Case #3
(image between C and F)
•
F
The first ray comes in parallel to the principal axis and reflects through the focus.
•
C

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principal axis
Concave Mirror Case #3
(image between C and F)
•
F
The first ray comes in parallel to the principal axis and reflects through the focus.us.
The second ray comes in through the focus and reflects parallel to the principal axis.
•
C

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principal axis
Concave Mirror Case #3
(image between C and F)
•
F
The first ray comes in parallel to the principal axis and reflects through the focus.us.
The second ray comes in through the focus and reflects parallel to the principal axis.
L - beyond C, O - inverted, S - larger than original, T - real
•
C

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principal axis
Concave Mirror Case #4
(image at F)
•
F
The first ray comes in parallel to the principal axis and reflects through the focus.
•
C

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principal axis
Concave Mirror Case #4
(image at F)
•
F
The first ray comes in parallel to the principal axis and reflects through the focus.us.
The second ray comes in through the focus but never reflects off the mirror.
Result - NO IMAGE is formed
•
C

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principal axis
Concave Mirror Case #5
(object between F and mirror)
•
F
•
C

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principal axis
Concave Mirror Case #5
(object between F and mirror)
•
F
The first ray comes in parallel to the principal axis and reflects through the focus.
•
C

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principal axis
Concave Mirror Case #5
(object between F and mirror)
•
F
The first ray comes in parallel to the principal axis and reflects through the focus.
The second ray comes through the focus and reflects parallel to the principal axis.
•
C

20. J.M. Gabrielse
principal axis
Concave Mirror Case #5
(object between F and mirror)
•
F
The first ray comes in parallel to the principal axis and reflects through the focus.
The second ray comes through the focus and reflects parallel to the principal axis.
The image forms where the rays converge. But they don’t seem to converge.
•
C

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principal axis
Concave Mirror Case #5
(object between F and mirror)
•
F
The first ray comes in parallel to the principal axis and reflects through the focus.
The second ray comes through the focus and reflects parallel to the principal axis.
The image is L - on the other side of the mirror, O - upright (the same direction as the
original, S - larger than the original, T - virtual (on opposite side of mirror)
•
C

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Convex Mirrors Case #6
(curved out)
Light rays that come in parallel to the principal axis reflect from the focus.
principal axis
•
F
The focus is considered virtual since sight lines, not light rays, go through it.
•
C

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Convex Mirrors Case #6
(example)
principal axis
•
F
•
F
•
C

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Convex Mirrors Case #6
(example)
principal axis
•
F
The first ray comes in parallel to the principal axis and reflects through the focus.
•
C

25. J.M. Gabrielse
Convex Mirrors Case #6
(example)
principal axis
•
F
The first ray comes in parallel to the principal axis and reflects through the focus.
The second ray comes through the focus and reflects parallel to the principal axis.
•
F
•
C

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Convex Mirrors Case #6
(example)
principal axis
•
F
The first ray comes in parallel to the principal axis and reflects through the focus.
The second ray comes through the focus and reflects parallel to the principal axis.
The light rays don’t converge, but the sight lines do.
•
F
•
C

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Convex Mirror Case #6
(example)
principal axis
•
F
The first ray comes in parallel to the principal axis and reflects through the focus.
The second ray comes through the focus and reflects parallel to the principal axis.
The light rays don’t converge, but the sight lines do.
L - other side of mirror, O - upright, S - smaller than original, T - virtual
•
C

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principal axis
Your Turn
(Convex Mirror)
•
C
• Locate the image and describe it
object
convex mirror
•
F

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principal axis
Your Turn
(Convex Mirror)
•
C
L - Other side of mirror, O - upright, S - smaller than original, T - virtual
object
convex mirror
image
•
F

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Thanks/Further Info
• Faulkes Telescope Project: Light & Optics by Sarah Roberts
• Fundamentals of Optics: An Introduction for Beginners by Jenny
Reinhard
• PHET Geometric Optics (Flash Simulator)
• Thin Lens & Mirror (Java Simulator) by Fu-Kwun Hwang