Magnification and Power of a Lens

Table of Contents

• Magnification of a Lens
• Power of a Lens
• Example
• Summary
• What’s Next?

In the previous segment, we looked at some Examples based on the lens equation. In this segment, let us learn about the magnification and power of a lens.

What is the Magnification of a lens?

• The magnification of a lens compares the size of the image to the size of the object.
• Magnification produced by a lens is defined as the ratio of the size of the image to the size of the object. It is denoted by ‘m’.
• Thus, if the heights of the object and the image are ℎ?

??? ℎ?

respectively, then ? = ℎ? .

ℎ?

• If m>1, then ℎ? > ℎ?. That is, the image formed is an enlarged image.
• If m<1, then ℎ? < ℎ?. That is, the image formed is a diminished image.
• For a concave lens, the image formed is always diminished. Thus, for a concave lens, m<1.

What is the Power of a lens?

• Consider two convex lenses such that one is thicker than the other. The focal length of the thicker convex mirror will be smaller than that of the thinner convex mirror. In the case of a thicker convex lens, the light bends more than that in the case of a thinner convex lens. That is, there is more deviation of light in the thicker convex lens than the thinner convex lens.
• Similarly consider two concave lenses such that one is thicker than the other. The focal length of the thicker concave mirror will be smaller than that of the thinner concave mirror. In the case of a thicker concave lens, the light bends more than that in the case of a thinner concave lens. That is, there is more deviation of light in the thicker concave lens than the thinner concave lens.