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Magnification: Applied Converging Lenses

Magnifying lenses are convex lenses. The magnification of a lens can be calculated by dividing the object height by the image height .

Do you recall how lenses work?

Pick the correct statement below.

What type of lens is a magnifying glass?

Magnifying glasses are convex lenses. In the image above, you can see one converging sun rays. At what distance, $x$ , from the lens is the sun? $f$ is the focal length.

A) $x>2f$ B) $2f>x>f$ C) $x<f$

Answer with A, B or C.

There are 4 ways a convex lens can create an image, depending on the distance away from the lens the object is. Now, consider using a magnifying glass to look at an ant. At what distance, $x$ , from the lens should the ant be in order to create an enlarged, virtual image? $f$ is the focal length.

Which description best fits the image created by a magnifying glass, when the object is within the focal length?

When we use a magnifying glass to enlarge an image, will the image be real or virtual?

The magnification of a lens compares the size of the image created by a lens to the size of the object.

If the image is larger than the object, then the magnification is larger than 1. If the image is smaller than the object then the magnification is less than 1. Can you work out which one is the correct equation for magnification then?

What do you think are the units of magnification?

A) The SI unit for height is $m$ B) Magnification is a ratio so it has no unit

Answer with A or B.

Calculate the magnification

The magnification describes the ratio of the object height and the image height, so it can tell us whether the image is enlarged or diminished.

What is the magnification if an image of a $4m$ tall tree is only $1m$ ?

Notice that for a diminished image, the magnification is smaller than 0.

Magnification will never be negative*,* because the values for the height of an object or image will never be negative.

To sum up!

Magnifying glasses are convex lenses.

These can produce different types of images, depending on where the object is placed relative to the lens.

The magnification of a lens can be calculated by using this equation

$magnification=\frac{image\:height}{object\:height}$

If the magnification is...

greater that 0, the image is enlarged. smaller than 0, the image is diminished.