Introductory Physics Volume Two
Introductory Physics Volume Two
Introductory Physics Volume Two
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8.7 Virtual Image in a Converging Lens 169<br />
⊲ Problem 8.2<br />
Using geometric arguments, prove the thin lens equations.<br />
⊲ Problem 8.3<br />
You have a lens with a focal length of 100cm. You place an object at<br />
150cm from the lens. The object is 3cm tall.<br />
(a) Construct the image location using the principle rays.<br />
(b) Find the location of the image using the thin lens equation.<br />
(c) Find the height of the image from the magnification equation.<br />
§ 8.7 Virtual Image in a Converging Lens<br />
You do not get a real image for all positions of the object. When<br />
the object distance is smaller than the focal length, you get a virtual<br />
image. You have probably notice this effect before while using a magnifying<br />
glass: if you look at something far away through a magnifying<br />
glass, you will se the object upside down. If you move closer to the<br />
object at some point it flips over and appears right side up.<br />
Virtual Image<br />
Real Image<br />
image<br />
paper<br />
lens<br />
paper<br />
lens<br />
image<br />
In the photograph above you can notice a few things. In the photo on<br />
the left, the letters on the page are almost in-focus, this means that<br />
the image is not too far from the page. In contrast, in the photo on the<br />
right, the letters on the page are very out of focus, this tells us that<br />
the image is far from the page. This is verified by the ray diagrams.<br />
Here is a larger diagram, showing the construction of the virtual<br />
image, that corresponds to the photo on the left.
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