1/u + 1/v = 1/f

1. When Object distance, u > 2*f, the lens is used by camera when forming images on film and the eyes.
2. When Object distance, u = 2*f, the lens is used by photocopier when making equal size copies.
3. When Object distance, f < u < 2*f, the lens is used by overhead projector to form magnified image.
4. When Object distance, u = f, the lens is used by spotlight when projecting parallel beam of light.
5. When Object distance, u < f, the lens is used by magnifying glass when viewing a enlarged image.

The magnification of the lens is given by: M = - v/u
where M is the magnification factor; if |M|>1, the image is larger than the object. Notice the sign convention here shows that, if M is negative, as it is for real images, the image is upside-down with respect to the object. For virtual images, M is positive and the image is upright.

Please note that the shape of the lens adjust with the focal length is for illustration purposes, it is not scientific.

This thin lens ray diagram java applet has:

Main view:

Lens that is controllable by the focal length f, +f imply converging lens -f imply diverging lens.
Focal points drag-able, 2F, F, F & 2F
u is position of Object from lens center c
v is position of Image from lens center c.
The object is drag-able to the right side of the lens

Top View:

dynamically display a possible use of the lens under different conditions with pictures shared under creative commons licenses and other similar pro usage licenses under attribution.

Bottom View:

4 radio buttons: allows for different visualization purposes of light path in the context of lens

1. no ray
2. principal-ray
3. marginal ray
4. all ray

4 check boxes:

1. "Real/Virtual?"
2. "Inverted/Upright?"
3. "Magnify/Diminish?"
4. "Same/Opposite side"

Auto-scale: to allow visualization view of images formed outside designed screen view.

3 slider control:

• u, object distance from c
• h, height of object f,
• focal length of lens

3 values display:

• v,image distance from c
• ih, image height
• M, Magnification

Activity:

Explore the simulation. Notice that you can move the sliders to vary the distance of the object to the center of the thin lens. What do each of the sliders, radio buttons and check-boxes do?
Take about 10 minutes to inquiry through the simulation model and describe the action of a thin converging lens on a beam of light. ( this simulation currently does not have beam of light)
Discuss with your lab partner what is the meaning of the focal length f.
hint: in terms of the way the light rays from the object is bend and pass through where?
check the principal rays radio button. Discuss and formulate ideas how the ray diagram allows the drawing of ray diagrams to illustrate the formation of real and virtual images of an object by a
thin converging lens.

1. What does the green ray light always do? 
2. What does the red ray light always do? 
3. What does the teal ray light always do? 

hint: in terms of the way ray light traveling parallel to and passing through where etc?
What does the term linear magnification mean in this simulation.
Discuss how it is calculated from?
How many ways are there to determine the magnification of the think converging lens.
Check the no ray radio button. move the sliders a suitable position of your choice. Now, sketch as accurately as possible on a piece of paper, the principal ray diagram ( minimum 2 rays) to get the image position and height. Practice a few times with different and varied examples to allow you to draw scale diagrams to deduce the focal length needed for particular values of magnification (converging lens only)
explore the simulation to make observations of the use of a single converging lens as a

1. magnifying glass
2. a projector 

Draw rays of examples for each case to show clearly how each forms an image

Suggested answers:

By definition, focal length is the distance between the point in the lens where the light begins to diverge (the nodal point) when the object is set at infinity.

Magnification M = - v/u = ih/h

Sample Learning Goals