Lesson 7

Mirrors 2 – Curved Mirrors

Curved MirrorsMirrors 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 TerminologyCurved 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 MirrorsA 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 MirrorsTo 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 smallerAttitude of image: oriented compared to object:

upright or invertedLocation of image: distance from mirror surfaceType 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 MirrorsConcave 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 OvensDevice 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.

Steps 1. Draw a line from the top of the object

straight (parallel to the PA) to the mirror surface. Then draw a line from there through the focal point.

2. Draw a line between the top of the object, the focal point and the mirror. At the point where the ray hits the mirror draw a straight line (parallel to the PA) away from the mirror.

3. Draw a line that goes from center of curvature, through the top of the object to the mirror and back.

S = LargerA = Upright L = Behind Mirror T = Virtual

Images formed by Concave Mirrors- Image in front of F

STEP 1STEP 2STEP 3

Concave Mirror – Image behind CSTEP 1STEP 2STEP 3

S. Smaller than object

A. Inverted

L. between C and F

T. Real

Summary of Images in a Concave Mirror

Convex MirrorsA 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 MirrorsBecause 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 MirrorsAll 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 DiagramSteps

1. 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.

Images formed by Convex Mirrors

STEP 1STEP 2 STEP 3

S = Smaller A = Upright L = Behind Mirror T = Virtual

More Examples: Concave Mirror – Image in between F and C

S = LargerA = Inverted L = Behind C T = Real

STEP 1STEP 2STEP 3

More Examples : Concave Mirror – Image at C

STEP 1STEP 2STEP 3

S. Same size as the Object

A. Inverted L. In front of Mirror

T. Real

Curved Mirror WorksheetWork on and hand in