Question

Write the differences between convex and concave lens.

Answer 1

Hint A lens is a piece of refracting medium that is bounded by two surfaces, at least one of which is a curved surface. The most common lenses are the spherical lenses, i.e., Convex and Concave lenses. We can use them separately or a combination of them as per our convenience.

Complete step-by-step answer:
Lenses can be broadly classified into two categories:

Convex Lens Some important characteristics of convex lenses are as follows:
- This lens is thick at the centre and thin at the edges.
- It is a converging type of lens.
- A convex has a real focus.
- It converges a parallel beam of light onto its focus on refraction through it.
- A ray of light passing through its focus becomes parallel to the principal axis after refraction.
- It always forms a real image except when the object is placed within its focus.
- If an object is placed within the focal length, a virtual image is formed.

Concave Lens Some important characteristics of concave lenses are as follows:
- This lens is thick at the edges and thin at the centre.
- It is a diverging type of lens.
- A concave lens has a virtual focus.
- It diverges a parallel beam of light so that it appears to be emerging from its focus.
- A ray of light appearing to meet its focus becomes parallel to the principal axis after refraction.
- It always forms virtual images.

Note The lenses can be differentiated easily by touching them with hands. If the centre is bulging outwards, it is a convex lens and if the centre is curved inwards, it is a concave lens.
Moreover, if the image is real, it must be a convex lens. And if the image is virtual then it is generally a concave lens but can be a convex lens in case the object distance is less than the focal length.
From magnifying glasses to other optical instruments like microscope, telescope, camera, etc., all work by the use of these lenses.