How to Draw Ray Diagrams

What is a Virtual Image?

A lens can form a virtual image just as a mirror does.

Rays from the same point on an object are bent by the lens so that they appear to come from a much larger object.

How Do Images Form from Lenses?

A converging lens can also form a real image.

In a real image, light rays from the object actually come back together.

A ray diagram is the best way to understand what type of image is formed by a lens, and whether the image is magnified or inverted.

These three rays follow the rules for how light rays are bent by the lens:

1. A light ray passing through the center of the lens is not deflected at all (A).

2. A light ray parallel to the axis passes through the far focal point (B).

3. A light ray passing through the near focal point emerges parallel to the axis (C).

To find where an image is formed, it is always necessary to follow at least two rays of light as they reflect from the mirror. The image formed by the flat mirror is a virtual image

Flat Mirror Ray DiagramsThe distance of the object from the

mirror (p)

is equal to the distance of the image from the mirror (q)

The size of the image is also equal to the size of the object.

Flat mirror ray diagrams

Object

mirror

Image

this distance (p)

equals this distance(q)

Object and image are the same size

Why are images reversed?

Ray diagrams can also explain why images appear backwards (left to right reversal)

Left side

mirror

Left side

Right Side

Right Side

What is Magnification?Magnification is the change in size

of image compared to object (doesn’t have to get bigger)

M = - q/p = h’/h

h is height

If a distance is on the virtual side it is negative.

M > 1 then image is bigger than object

M < 1 then image is smaller than object

M = (+) upright

M = (-) upside down