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MIRRORS AND
LENSES
PREPARED BY: TYPE YOUR NAME HERE

MIRRORS
• Mirrors form images using the property of light
called reflection, unlike lenses which form images
using refraction.
• Mirrors are smooth reflecting surfaces.
• A plane mirror is a flat surface. Usually it is glass
coated with a reflective metallic substance.

PLANE MIRRORS
• A ray diagram is used to
determine the location of the
image in a mirror or lens.
• The image in a plane mirror
appears to be behind the
mirror.
• The rays of light diverge at the
location of the image.
• When the rays diverge, the
image is called a virtual image.

PLANE MIRRORS
• Notice the distance of the
object and image from the
mirror. For a plane mirror,
do = di
• The height of the image is
another important feature.
For a plane mirror,
ho = hi
• The ratio of hi/ho is called
magnification.

PLANE MIRRORS
•Plane mirrors form virtual images.
•Image distance is equal to object
distance. do = di
•Magnification = 1

EXAMPLE
•What is the minimum vertical
length of a plane mirror needed
for a person to see a complete
head to toe image of himself?

SPHERICAL MIRRORS
•Spherical mirrors are reflecting
surfaces with spherical geometry.
•For reflections on the inside
surface, the mirror is called concave.
•For reflections on the outside
surface, the mirror is called convex.

CONCAVE MIRRORS
• Concave mirrors focus light
at a single point.
• Light rays that travel parallel
to the mirror reflect through
the focal point.
• The focal point is half of the
radius of curvature.
• Since light rays converge, the
image formed is real. You
could project an image on a
carefully placed card.

CONCAVE MIRRORS – RAY
DIAGRAMS
• Optical Axis - a line through the center of
the mirror that intersects the surface of the
mirror.
• Center of Curvature – center of the circle
• Focal point – the point at which reflected
rays intersect

RAY DIAGRAMS
• Draw the mirror, the optical axis, the center of
curvature,and the focal point.
• Draw the object at the appropriate position.
1. Draw the first ray from the object to the mirror parallel to the
optical axis, and reflecting through the focal point.
2. Draw the second ray through the center of curvature.
3. A third ray travels from the object through the focal point and
to the mirror. It reflects parallel to the mirror.
• An image will be formed where the rays converge.

CONCAVE MIRROR RAY DIAGRAM
•Notice the object is
placed beyond C.
•Three rays are drawn.
•The image is real,
inverted, located
between C and F, and
reduced.

CONCAVE MIRRORS – THREE SITUATIONS
• If do >C, then f<di<C
and is real, reduced,
inverted.
• If f<do<C, then di>C and
is real, inverted, and
enlarged. (no picture)
• If do <f, then image is
virtual and enlarged.

MIRROR EQUATIONS
• The image and object distances are related by
• The magnification can be found using

SIGN CONVENTIONS FOR
SPHERICAL MIRRORS

EXAMPLE
•A concave mirror has a radius of
curvature of 30cm. If an object is
placed a)45cm b) 20 cm c) 10 cm
from the mirror, where is the image
formed and what are its
characteristics?

EXAMPLE
• An object is placed 20cm in front of a
diverging mirror that has a focal length
of -15cm. Use a ray diagram to
determine whether the image formed
is real or virtual. Find the location of
the image using equations.

SPHERICAL ABERRATIONS
• Spherical mirrors focus
light well for small
angles of incidence (and
reflection) but produce
blurry images for larger
angles of incidence.
• Parabolic mirrors focus
parallel rays from
distant objects at one
focal point.

LENSES
• Lenses focus light by refracting light to form an
image.
• Biconvex lenses are convex on both surfaces
and cause rays to converge.
• Biconcave lenses are concave on both surfaces
and cause light to diverge.

THREE RAYS TO DRAW!
• First ray: parallel to optical axis and refracting
through focal point.
• Second ray: called the chief ray passes from the
object through the center of the lens un-refracted.
• Third ray: through the focal point and refracting
parallel to optical axis.

LENS RAY DIAGRAM
• If object is beyond the
focal point, a real
inverted image if
formed.
• If the object is between
the focal point and the
lens, a magnified virtual,
upright image is formed

CONCAVE LENSES
• Concave lenses form
virtual images.

LENS EQUATIONS
• Are exactly the same as mirror
equations!

EXAMPLE
• An object is 30 cm in front of a
biconvex lens of focal length 20 cm.
Use a ray diagram to locate the
image. Discuss the characteristics of
the image.

HOMEWORK
• Pg 755 # 45, 49, 54, 55, 59, 62, 63, 69
– 71, 75
• Begin to prepare for Ch 22,23 exam
on MONDAY.

COMBINATIONS OF LENSES
• The image of the first lens becomes the object of
the second lens!
• If the image of the first lens is on the opposite side
of the second lens, consider the image of the first
lens to be a virtual object for the second lens and do
becomes negative.
• Magnification of the total Mtot = M1M2

G10 Science Q2-Week 8- Properties of Mirror.ppt

EXAMPLE
• Consider two lenses similar to those
illustrated in fig 23.19. Suppose the object
is 20 cm in front of lens L1 which has focal
length of 15 cm. Lens L2, with focal length
of 12 cm, is 26 cm from L1. What is the
location of the final image?

CONTENT, IMAGES, TEXT, ETC. USED BELONG TO THE RIGHTFUL
OWNER. NO COPYRIGHT INFRINGEMENT INTENDED.

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G10 Science Q2-Week 8- Properties of Mirror.ppt

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