CK-12-Physics - Intermediate

http://www.ck12.org Chapter 20. Geometric Optics

FIGURE 20.20

Sign conventions for diverging lenses (single lens system)

1. Distances are measured from the lens.


2. The focal length is negative.


3. The object distance is positive.


4. The image distance is negative.


5. The object height is always positive. The image height is positive.

Concluding remarks for diverging lenses

Regardless of where an object is placed, a diverging lens will form only virtual, upright, reduced images.

http://demonstrations.wolfram.com/RayTracingWithLenses/

Illustrative Example 21.4.2

An object of height 7.0 cm object is placed 35.0 cm from a diverging lens of focal length -14.0 cm (seeFigure
20.17.).

a. Find the image position.

Solution:

We are givenho= 7. 0 cm,do= 35. 0 cm, andf=− 14. 0 cm.

Using the Lens Equation,

1

do

+

1

di

=

1

f

→

1

35. 0

+

1

di

=−

1

14. 0

→

1

di

=−

1

14. 0

−

1

35. 0

=−

35. 0 + 14. 0

490 cm

→

di=− 10. 0 cm

The image distance is negative, as it should be for a diverging lens. The image is virtual.