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A Convex Lens as a Magnifying Glass.

The type of image made by a convex lens
depends on how far away the object is.

The picture below shows how to draw a ray diagram
for an object that is nearer to the lens than F.
Click here for a ray diagram for
an object that is further away than F.

When the object is nearer to the lens than F
(less than the focal length)
a convex lens acts as a magnifying glass.


What is the Ray Diagram for a Magnifying Glass?

The bottom of the object is placed on the principle axis.
Two rays of light are drawn from the top of the object.
The first ray of light is parallel to the principle axis
and therefore passes through the focal point.
The second ray of light goes from the top of the object
and passes straight through the centre of the lens.

Ray Diagram for a Magnifying Glass

Unlike the previous page, the rays are
diverging (moving apart) on the right side of the lens.
The eye looks back along the rays that seem to have come
from a point behind the object where the two rays of light cross.
This is where you draw the top of the image.
The bottom of the image is still on the principle axis.

The image made by a magnifying glass
is virtual, upright and bigger than the object.

The image is called virtual because the light rays
really go there (compare this with a real image).
The virtual light rays are drawn as dotted lines.
The image is called upright because it is the right way up
(compare this with an inverted image).
The image is bigger than the object
and on the same side of the lens as the object.

The eyepiece of a telescope is
a convex lens used as a magnifying glass.

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