-
When Object distance, u > 2*f, the lens is used by camera when
forming images on film and the eyes.
-
When Object distance, u = 2*f, the lens is used by photocopier when
making equal size copies.
-
When Object distance, f < u < 2*f, the lens is used by overhead
projector to form magnified image.
-
When Object distance, u = f, the lens is used by spotlight when
projecting parallel beam of light.
-
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
-
no ray
-
principal-ray
-
marginal ray
-
all ray
4 check boxes:
-
"Real/Virtual?"
-
"Inverted/Upright?"
-
"Magnify/Diminish?"
-
"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.
-
What does the green ray light always do?
-
What does the red ray light always do?
-
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
-
magnifying glass
-
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