**Evans SPH 3U1**

**Physics Grade
11**

**Unit 3: Light
and Optics**

**Note 9:
Calculations with Lenses**

Reference: Chapter 11.9

**Thin lens Formula:**

**Magnification,m:**

where:

d_{o} is the distance
between the object and the lens

d_{i }is the distance
between the image and the lens

f is the focal length

h_{i} is the height of
the image

h_{o} is the height of
the object

**Sign Conventions:**

h_{o }
height of object must be positive

d_{o }distance to
object must be positive

f positive for convex lens, negative for concave

h_{i}
positive if image is upright, negative if image is inverted

d_{i
}negative if image is on same side (virtual), positive if image is on
opposite side (real)

**Example 1**: a converging
lens is being used as a magnifying glass. If the focal length of the lens is
15cm and an ant that is 10cm away is being viewed, find the location of the
image and its magnification.

(you'll find di is negative 30cm which means the image is on the same side of the lens as the object. It is a virtual image. The image is larger than the object and it is right side up)

**Pg. 395 #'s 70, 73, 74, 76**

**Quiz**