An object in front of a curved mirror gives off light in all different directions. Most miss the mirror so don’t make an image. Many, many, many light.

An object in front of a curved mirror gives off light in all different directions. Most miss the mirror so don’t make an image. Many, many, many light rays do hit and follow the law of reflection. A well-shaped mirror directs all of those reflected light rays so that they can be traced back to a single point.

Since all of the light rays point to the same place, we don’t have to use all of them, we just need to find three light rays that are easy to draw and find the point they seem to come from. We then know that any reflected ray will look like it comes from that point and that is where the image appears to us.

To understand how these special rays work, we need to know two things about a curved mirror’s geometry.

First, every curved mirror has a central axis that “cuts” directly through the middle of the mirror and indicates where the mirror faces.

Axis

Second, there is a special point on the axis where all light rays coming directly into the mirror (parallel to the axis) cross the axis after they are reflected – known as the focal point. The focal point is located at the midpoint between the surface of the mirror and its center of curvature (the center of circle that defines the mirror’s shape.

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Focal Point

Center of Curvature

The first special ray leaves the object traveling parallel to the axis and reflects off the mirror heading through the focal point.

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The second special ray leaves the object traveling through the focal point and reflects off the mirror heading parallel to the axis.

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The third special light ray that passes through the center of curvature hits the mirror directly and bounces directly back, along the same line through the center of curvature.

Drawing a Concave Mirror Ray Diagram

Step #1: Incoming light ray parallel to axis – Outgoing on trajectory through focal point

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Object beyond focal point

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Drawing a Concave Mirror Ray Diagram

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Step #2: Incoming light ray through focal point – Outgoing parallel to axis

Object beyond focal point

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Drawing a Concave Mirror Ray Diagram

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Step #3: Incoming light ray through center of curvature – Outgoing through center of curvature

Object beyond focal point

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Drawing a Concave Mirror Ray Diagram

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Step #4: Draw image where reflecting lines (real or imaginary) meet.

IMAGE IS:• Inverted• Real• Smaller than object•Closer to mirror

Object beyond focal point

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Drawing a Concave Mirror Ray Diagram

Step #1: Incoming light ray parallel to axis – Outgoing on trajectory through focal point

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Object between center of curvature and focal point

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Drawing a Concave Mirror Ray Diagram

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Step #2: Incoming light ray through focal point – Outgoing parallel to axis

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Object between center of curvature and focal point

Drawing a Concave Mirror Ray Diagram

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Step #3: Incoming light ray through center of curvature – Outgoing through center of curvature

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Object between center of curvature and focal point

Drawing a Concave Mirror Ray Diagram

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Step #4: Draw image where reflecting lines (real or imaginary) meet.

IMAGE IS:• Inverted• Real• Larger than object• Further from mirror

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Object between center of curvature and focal point

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Drawing a Concave Mirror Ray Diagram

Step #1: Incoming light ray parallel to axis – Outgoing on trajectory through focal point

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Object within focal point

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Drawing a Concave Mirror Ray Diagram

Step #2: Incoming light ray “through” focal point – Outgoing parallel to axis

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Object within focal point

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Drawing a Concave Mirror Ray Diagram

Step #3: Incoming light ray “through” center of curvature – Outgoing through center of curvature

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Object within focal point

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Drawing a Concave Mirror Ray Diagram

Step #4: Draw image where reflecting lines (real or imaginary) meet.

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IMAGE IS:• Upright• Virtual• Larger than object• Further from mirrorObject within focal point

Drawing a Convex Mirror Ray Diagram

Special Ray #1: Incoming light ray parallel to axis – Outgoing on trajectory through focal point

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Drawing a Convex Mirror Ray Diagram

Special Ray #2: Incoming light ray toward focal point – Outgoing parallel to axis

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All objects

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Drawing a Convex Mirror Ray Diagram

Special Ray #3: Incoming light toward center of curvature – Outgoing “through” center of curvature

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All objects

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Drawing a Convex Mirror Ray Diagram

Step #1: Incoming light ray parallel to axis – Outgoing on trajectory through focal point

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All objects

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Drawing a Convex Mirror Ray Diagram

Step #2: Incoming light ray toward focal point – Outgoing parallel to axis

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All objects

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Drawing a Convex Mirror Ray Diagram

Step #3: Incoming light ray toward center of curvature – Outgoing through center of curvature

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All objects

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Drawing a Convex Mirror Ray Diagram

Step #4: Draw image where reflecting lines (real or imaginary) meet.

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IMAGE IS:• Upright• Virtual• Smaller than object• Closer to mirro

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All objects

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