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This post is for Standard Grade and Intermediate 2.

Here we consider an object closer than one focal length.  You will see that it is not possible to obtain a real image when the object is this close to the lens.  On a ray diagram, a real image is one that is found on the other side of the lens from the object.

Real images can always be displayed on a screen – a projector in the cinema or classroom produces a real image.  If you are doing an experiment, you can check to see if an image is real using a piece of paper.  Move your sheet of paper closer to and further from the lens – if you can’t get an image to form on the paper then the image must be virtual.  When we look at an object up close through a magnifying glass, we see a virtual image.

ray diagram for objects closer than 1f from mr mackenzie on Vimeo.

Podcast Video [ 2:41 ] Download

If you are sitting Credit Standard Grade or Intermediate 2 you should be able to draw a ray diagram for a convex lens.

At Standard Grade you must be able to draw this diagram for a magnifying glass.  A video for this will be posted shortly.

Intermediate 2 candidates may be asked to draw the diagram for an object placed

• closer than one focal length
• between one and two focal lengths
• more than two focal lengths

from the convex lens.  I will post a video showing each of these three situations.

Let’s start with an introduction to drawing ray diagrams.  This video looks at an object between one and two focal lengths from the lens.  It will show you how to draw the diagram and explain the terms we use to describe the image.

how to draw a ray diagram from mr mackenzie on Vimeo.

Disclaimer: No rabbits were harmed in the making of this video.

Podcast Video [ 3:57 ] Download