How do you draw a converging lens ray diagram?

A converging lens ray diagram can be drawn with three principle rays. However, the type of image will change (as will the ray diagram) depending upon whether the object is inside or outside of the focal length. Let’s start with an object outside of the focal length.

  1. The first ray is drawn straight towards the lens from the top of the object, then converges through the focal point on the opposite side (top ray in the image above).

  2. The second ray is drawn from the top of the object straight through the center of the lens (middle ray above).

  3. The last ray is drawn from the top of the object through the focal point on the same side, then drawn parallel to the axis as it emerges from the other side.

The point where the lines meet on the opposite side of the object (real image) is the top of you image with the bottom at the axis.

What about when the object is inside the focal length? Here the rays exit the lens diverging, which means they converge at a point behind the lens on the same side as the object. They must therefore be traced back (virtual image).

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