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1. 1
Exercise: Image properties formed by lenses.
The purpose of the following investigation is to demonstrate various characteristics of the
types of images formed by convex and concave lens. The object (the arrow on the right)
will be placed at various distances from the lens as a thought exercise and we will use the
rules of image formation to find where the image would form and how to describe it.
Object Distance the distance from the object to the center of the lens.
Image Distance the distance from the image to the center of the lens.
Size of Image the image may appears larger, the same size, or smaller than
the object.
Image Location whether the image appears on the same side of the lens as the
object or on the opposite side of the lens. This amounts to:
do you have to look through the lens to see it, or can you
focus the image on a screen?
Orientation of Image whether the image is upright or inverted
Type of Image whether the image is real or virtual
When light rays from an object pass through a lens, they may converge to form an image on the
other side of the lens or they may diverge.
• If the light rays converge to form an image, the image is called a real image. A real
image can be projected onto a screen. A real image will be inverted relative to the
object.
• If the light rays diverge from the lens, they will not focus on a screen. The image that is
formed is a virtual image. A virtual image will appear on the same side as the object;
i.e. you have to look through the lens to see it. A virtual image will be upright relative
to the object.
TO FORM AN IMAGE, YOU NEED TWO OF THE THREE RAYS:
• First, mark the focal point (f) on the right side of the lens!
For CONVERGING lenses:
1. A parallel ray from the tip of the arrow will converge to the focal point on the
right side of the lens.
2. A ray through the center of the lens continues unchanged.
3. A ray through the focal point on the left will become parallel after hitting the lens.
For DIVERGING lenses:
1. A parallel ray from the tip of the arrow will diverge on the right side of the lens as
if emanated from the focal point on the left.
2. A ray through the center of the lens continues unchanged.
3. A ray through the focal point on the left will become parallel after hitting the lens.

2. 2
Case 1 Convex lens: The object distance is greater than two focal lengths. (o > 2f)
Case 2 The object distance is equal to two focal lengths. (o = 2f)
Case 3 The object distance is between one and two focal lengths. (f < o < 2f)
Case 4 The object distance is equal to one focal length. (o = f)
Case 5 The object distance is less than one focal length. (o < f)
Case 6 The concave lens - The object can be located anywhere.
f2f
object
f2f
object
f2f
object
f2f
object
f2f
object
f2f
object

3. 3
Data Table. Focal length = ______________(measure with a ruler)
Case Object
Distance
Image
Distance
Object
Height
Image
Height
Size of
Image
Image
Location
Orientation
of Image
Type of
Image
o>2f
1
o = 2f
2
f<o<2f
3
o=f
4
5
o<f
6
o=any
distance
QUESTIONS (Applies to cases 1 through 5 ONLY)
1. What is the relationship between the object distance and the focal length when a real
enlarged image is formed?
________________________________________________Case(s)____________
2. What is the relationship between the object distance and the focal length when a
virtual image is formed?
________________________________________________Case(s)____________
3. If a virtual image is formed, is the image larger or smaller than the object?
________________________________________________Case(s)____________

4. 4
4. What is the object distance when no image is formed?
________________________________________________Case(s)____________
5. If a real image is formed, is the image upright or inverted?
________________________________________________Case(s)____________
6. If a virtual image is formed, is the image upright or inverted?
________________________________________________Case(s)____________
7. In general, where are real images formed, on the same side of the lens as the object
or on the opposite side?
________________________________________________Case(s)____________
8. In general, where are virtual images formed, on the same side of the lens as the
object or on the opposite side?
________________________________________________Case(s)____________
9. What is the relationship between the object distance and the focal length when a real
smaller image is formed?
________________________________________________Case(s)____________
10. What is the relationship between the object distance and the focal length when a real
image the same size as the object is formed?
________________________________________________Case(s)____________