Transcript urved - St. Thomas Aquinas Catholic Secondary School

Mirrors 2 – Curved Mirrors
Lesson 7
December, 2011
St. Thomas Aquinas – Physics (the best)
Curved Mirrors
 Mirrors with a single curvature find many uses in our homes
and optical devices. Two types of curved mirrors
 Concave (converging)
 Convex (diverging).
Curved Mirrors
Curved Mirror Terminology
 Curved mirrors also obey the law of reflection.
 When parallel light rays strike a curved surface, each ray
of light will reflect at a slightly different position. All of
these rays eventually meet at a common point.
 The point where light rays meet, or appear to meet, is called
the focal point, F
Curved Mirror Terminology
 Vertex (V)- The middle point of a curved mirror
 Centre of curvature (C) if the mirror were extended to be
a circle/sphere, this point would be the centre.
Curved Mirror Terminology
 The principal axis (PA)is an imaginary line drawn
through the vertex, perpendicular to the surface of
the curved mirror.
Curved Mirror Terminology
 The distance between the vertex and the object is
represented by do.
 The distance between the vertex and the image is di.
Curved Mirror Terminology
 The height of the object is ho,
 The height of the image is hi.
 The focal length, f, is the distance from the vertex to
the focal point of a curved mirror.
 If the object is farther away from the mirror than
the focal point, the reflected rays form a real
image.
 A real image is an image formed by light
rays that converge at the location of the
image.
Concave Mirrors
 A concave mirror, also called a converging mirror,
has a surface that curves inward like a bowl
 The image formed by a concave mirror depends on how far
the object is from the focal point of the mirror.
 The image can be larger or smaller than the object as well as inverted
or upright and real or virtual
Concave Mirrors
 To explain the size, location and type of image, the acronym




S.A.L.T is used.
Size of image: compared to the object: same, larger, or
smaller
Attitude of image: oriented compared to object: upright or
inverted
Location of image: distance from mirror surface
Type of image: real or virtual (A real image is formed when
the light actually arrives at the image location.)No real image
forms in a plane mirror.
Some Uses for Concave Mirrors
 Concave mirrors are specially designed to
collect light and bring it to a single point.
Some Uses for Concave Mirrors
 Used in telescopes to collect light rays from a great distance and
bring them together.
 flashlights, car headlights, dental examination lights, and other
applications
Solar Ovens
 Device that uses light from the Sun as its energy
source to heat or cook food.
 A solar oven uses a concave mirror to concentrate the Sun’s
rays, converting light to heat through absorption if the
interior of the oven is a dark colour, and using a clear cover
so that the Sun’s rays can enter but very little heat can leave.
Drawing a Concave Mirror Ray Diagram
1. Use an upright arrow to represent the object
2. Show real rays as solid lines.
3. Use dashed lines to present virtual rays, which
are rays that only appear to exist behind the
mirror.
Images formed by Concave Mirrors
- Image in front of F
STEP
12
STEP
STEP 3
 S = Larger A = Upright
L = Behind Mirror T = Virtual
Concave Mirror – Image behind C
STEP
12
STEP
STEP 3
S. Smaller A.
than object Inverted
L. In front T. Real
of mirror
Summary of Images in a Concave
Mirror
Convex Mirrors
 A mirror with a surface curved outward is a convex
mirror, also called a diverging mirror
 A convex mirror spreads out the rays.
Uses for Convex Mirrors
 Because convex mirrors allow you to see more than plane
mirrors, they are often used for security in stores as well as
rear-view mirrors in cars.
Images Formed by Convex Mirrors
 All images in a convex mirror are virtual.
 The reflected light rays never meet and the image
appears to come from behind the mirror.
Drawing a Convex Mirror Ray Diagram
Steps
Draw a line from the top of the object straight across (parallel to
the principle axis) to the mirror. Then draw a dotted line from
there to the focal point. This line is also drawn as a solid line on
the outside of mirror as it moves away from the mirror surface.
2. Draw a line from the top of the object to the center of curvature.
Once the line reaches the mirror it becomes dotted.
3. Draw a line from the top of the object to the vertex. The
reflected ray will leave the mirror at the same angle as the
incident ray angle. Extend the reflected ray as a dotted line
behind the mirror
 The point at which all the lines meet is where the top of the virtual
image is located.
1.
Images formed by Convex Mirrors
STEP
12
STEP
STEP 3
S = Smaller
A = Upright
L = Behind Mirror
T = Virtual
More Examples: Concave Mirror –
Image in between F and C
STEP
1 2
STEP
STEP 3
 S = Larger A = Inverted L = In front of Mirror T = Real
More Examples :
Concave Mirror – Image at C
STEP
12
STEP
STEP 3
S. Same size as the A. Inverted L. In front of
Object
Mirror
T. Real
Curved Mirror Worksheet
 SNC 2D work on practice sheets and homework
 SALT – Pg 492
 Pg 493#1-9
Pg 501#1-10
 Pg 497 – Figure 6 Concave Review
 Pg 499 – Table 1 Convex Review
 SNC 2P work on worksheets and homework
 Respect Mr. Eagan and Mr. Donato