converging and diverging lenses
PriWowo12
GeometricOptics_Lenses1.pdf
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PHYS1110L
Converging and Diverging Lenses
Principles
The thin lens equation is as for curved mirrors.
The equation for magnification is:
Convex lenses can produce real images if the object is placed outside the focal point or virtual
images if the object is inside the focal point. Concave lenses always produce virtual images.
With lenses the object distance, do, is positive if the object is in front of the lens and negative if it
is in back of the lens. The image distance, di, is positive if the image is in back of the lens and
negative if it is in front of the lens. In other words, if the rays from the object pass through the
lens and converge, the object and image will be on opposite sides of the lens, do and di will have
the same sign, and the image will be real. If the rays from the object diverge, the object and
image will be on the same side of the lens, do and di will have opposite signs, and the image will
be virtual.
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Procedure and Data
Access the simulation using the following web link
https://phet.colorado.edu Select Simulations on the menu bar and then select Physics. Select the Geometric Optics lab and then select the arrow in the middle to launch. Select the Lens once the lab has launched.
Select the Principle rays (bottom menu) and Ruler (You will physically move the ruler to the simulation). Click on the “change object” until you see an pencil as the object.
Note down the following parameters:
Curvature Radius:………………………
Refractive index:……………………….
Diameter:……………………..
The horizontal axis through the center of the lens is called the principle axis. The pencil on the
left hand side is your object and the image is appearing on the right hand side. Move the Object
(pencil), so the eraser of the pencil lay on to the principle axis.
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The “X”s on the principle axis represents the focal point of the lens. The distance from lens to the
focal point is called the focal length (f). The focal length is equal in either side of the lens.
Measure the focal length using the ruler tool
Focal length (f):………………….
Calculate 1/f :……………………………..
The distance between the object and the lens is called the object distance (d0) and the distance
between the lens and the image is called the image distance (di). Set the object distance to the given
values in the table below, and record the image distance. And do the appropriate calculations to
fill out the rest of the table. Note: measure the distances from the center of the lens. You can move
either the object or the lens.
d0 di 1/d0 1/di 1/d0 +1/di
200 cm
180 cm
150 cm
100 cm
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How did the 1/f compare with the values in the last column in the table?..............................
What happen to the image size when the object distances decrease?
………………………………………………………………………………………………………
………………………………………………………………………………………………………
…………………………………………………………………………………………….
In all the above cases the object is placed further than the focal length. Now set the object distance
to 40 cm, so the object is in between the focal point and the lens.
What happed to the image? Can you see it?......................................
Click and put a check Virtual image on the top menu. Can you see the image now?................
Re-do the measurements with following object distances. Note: consider the image distance as a
negative value.
d0 di 1/d0 1/di 1/d0 +1/di
20 cm
40 cm
50 cm
60 cm
How did the 1/f compare with the values in the last column in the table?..............................
What happen to the image size when the object distances increases?
………………………………………………………………………………………………………
………………………………………………………………………………………………………
…………………………………………………………………………………………….
Place the object on the focal point. What can you say about the light rays? Are there going to cross
each other at any point?
……………………………………………………………………………………
Change the curvature of radius (R), and observe what happens to the focal length (f).
curvature of radius (R) focal length (f)
0.3
0.5
0.8
5
1.3
Change the refractive index, and observe what happens to the focal length (f).
the refractive index focal length (f)
1.2
1.43
1.52
1.7
Does the diameter effect on the focal length?
………………………………………………………………………………………………………
………………………………………………………………………………………………………
………………………………………………………………………………………………………
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