Everything Science Grade 11

CHAPTER 13. GEOMETRICAL OPTICS 13.2

1

f

=

1

do

+

1

di

1

4

=

1

6

+

1

di

1

4

−

1

6

=

1

di

3 − 2

12

=

1

di

di = 12 cm

Step 3 : Calculate the magnification

m =−

di

do

=−

12

6

=− 2

Step 4 : Write down the properties of the image

The image is real, diis positive, inverted (because the magnification is negative)

and enlarged (magnification is > 1)

Example 2: Locating the image position of a convex lens:I

QUESTION

An object is placed 5 cmto the left of a converging lens which has a focallength of 2,5 cm.

1. What is the positionof the image?


2. Is the image real or virtual?

SOLUTION

Step 1 : Set up the ray diagram

Draw the lens, the object and mark the focal points.

Object F 1

F 2

O

Step 2 : Draw the three rays