What is a Lens
A lens is a curved and polished piece of glass or any other transparent material.
The most common place where you will find lenses is in spectacles. You will also find lenses in magnifying glasses, binoculars, and in cameras.
Fig. Lenses used in spectacles
Common lenses are of two types: convex and concave.
A convex lens is thicker in the middle than at the edges. A magnifying glass is a convex lens.
A concave lens is thicker at the edges than in the middle. Things look smaller through a concave lens.
The light falling on the lenses can be represented by rays. Parallel rays falling on a convex lens converge to a point known as the principal focus (F).
In a concave lens, parallel rays appear to diverge from the principal focus, whereas in a convex lens, parallel rays converge to the principal focus. Due to this, convex and concave lenses are also known as converging and diverging lenses, respectively.
We have already studied about images formed by concave and convex mirrors. Let us now see the different kinds of images formed by convex and concave lenses.
The nature of the image formed by a convex lens [Fig. 15.10(a)] varies as the distance of the object from the lens changes. However, with a concave lens, we always get virtual, upright, and diminished images (regardless of the distance of the object from the lens) [Fig. 15.10(b)].
Given below is the representation of the above images using ray diagrams.
Images Formed by a Convex Lens
A convex lens forms a variety of images, depending on where the object is placed with respect to the lens. The position of the object can be specified with respect to the principal focus of the lens (Fig. 15.9). The nature of the images formed by a convex lens is given in Table 15.2.
People also ask