Images in a Concave Mirror

There are an infinite number of light rays that radiate our from an object.

We only have to keep track of a few light rays to be able to find an image created by an optical device.

There are four light rays that are fairly easy to follow for a concave mirror.

Reflection from a Concave Mirror

1. Light rays that are parallel to the principal axis reflect through the focal point.

2. Light rays that pass through the focal point before hitting the mirror pass reflect from the mirror and go back out parallel to the principal axis.

3. Light rays that travel through the centre of curvature reflect straight back through the centre of curvature.

4. Light rays that hit the mirror at the vertex reflect so that the angle of incidence is equal to the angle of reflection.

Reflection from a Concave Mirror

The four rays can be used to find the characteristics of the image. (An image occurs when an object can be seen using an optical device like a mirror or a lens.)

There are four characteristics of any image.

Locating Images

Size◦An image can be larger

than the object, or smaller than the object, or the same size as the object.

Attitude◦An image can be upright or

inverted (upside down).

Using “SALT” to Describe an Image

Location◦The location can be described relative to the object

and the optical device and the focal point.Type

◦Images can be real or virtual. A real image can be projected on a screen and seen by the eye. A virtual image can only be seen by the eye, but a virtual image cannot be projected on a screen.

Camera Obscura

Reflection from a Concave MirrorObject Beyond the Centre of Curvature

C F

Reflection from a Concave MirrorObject Beyond the Centre of Curvature

C F

Reflection from a Concave MirrorObject Beyond the Centre of Curvature

C F

Reflection from a Concave MirrorObject Beyond the Centre of Curvature

C FimageThe image is smaller, inverted, real, and between the

Focal Point and the Centre of Curvature.

Reflection from a Concave MirrorObject between C and F

C F

Reflection from a Concave MirrorObject between C and F

C F

Reflection from a Concave MirrorObject between C and F

C F

Reflection from a Concave MirrorObject between C and F

C F

image

The image is larger than the object, inverted, beyond the Centre of Curvature and real.

Reflection from a Concave MirrorObject at the focal point

C F

Reflection from a Concave MirrorObject at the focal point

C F

Reflection from a Concave MirrorObject at the focal point

C F

Reflection from a Concave MirrorObject at the focal point

C F

Reflection from a Concave MirrorObject at the focal point

C F

Reflection from a Concave MirrorObject at the focal point

C F

The light rays do not converge, but remain parallel.Flashlights, headlights, and spot lights use concave mirrors and place the light at the focal point.

Reflection from a Concave MirrorObject between F and the mirror

C F

Reflection from a Concave MirrorObject between F and the mirror

C F

Reflection from a Concave MirrorObject between F and the mirror

C F

Reflection from a Concave MirrorObject between F and the mirror

C F

Reflection from a Concave MirrorObject between F and the mirror

C F

Reflection from a Concave MirrorObject between F and the mirror

C F

The light rays reflected from the mirror diverge. We can follow the light rays back behind the mirror.

Reflection from a Concave MirrorObject between F and the mirror

C F

Reflection from a Concave MirrorObject between F and the mirror

C F imageThe image is larger, right-side up, behind the mirror, and virtual.

Reflection from a Convex MirrorThe centre of curvature and the focal point are both behind the mirror.

C F

Reflection from a Convex MirrorThe centre of curvature and the focal point are both behind the mirror.

C FA light ray from the object heads towards the focal point. It hits the mirror and it reflected out parallel to the principal axis.

Reflection from a Convex MirrorThe centre of curvature and the focal point are both behind the mirror.

C F

Reflection from a Convex MirrorThe centre of curvature and the focal point are both behind the mirror.

C FA light ray from the object heads towards the centre of curvature. The light ray reflects straight back.

Reflection from a Convex MirrorThe centre of curvature and the focal point are both behind the mirror.

C F The reflected rays diverge. We can follow the rays back behind the mirror.

Reflection from a Convex MirrorThe centre of curvature and the focal point are both behind the mirror.

C F The reflected rays diverge. We can follow the rays back behind the mirror.

Reflection from a Convex MirrorThe centre of curvature and the focal point are both behind the mirror.

C F

Reflection from a Convex MirrorThe centre of curvature and the focal point are both behind the mirror.

C F image

The image is smaller, right-side up, behind the mirror, and virtual.

For a mirror that is spherical, light rays parallel to the principal axis will only reflect through the focal point if a small portion of the curve is used.

Beyond the small portion of the curve, rays parallel to the principal axis will not pass through the focal point. This is the spherical aberration.

Mirrors that are the shape of parabolas prevent this from happening.

Spherical Aberration

Mirror Equations

Magnification Equation◦ or

Mirror and Magnification Equations