Hey so simple.
real image is formed by convex lens only
whereas concave lens forms only virtual images.
keep an object beyond focus, if image formed is real and inverted then it is convex lens and if image is virtual and erect then it is concave lens

Distinguishing between a Convex and Concave Lens based on the Nature of Image Formed

To distinguish between a convex and a concave lens based on the nature of the image formed, we need to understand the properties and behavior of these lenses. The nature of the image formed by a lens can be determined by observing the behavior of light rays passing through it and the characteristics of the lens itself.

Convex Lens:
A convex lens is thicker at the center and thinner at the edges. It converges or brings the light rays together after refraction. The image formed by a convex lens can be classified as either real or virtual.

Real Image:
- A real image is formed when the incident light rays converge and actually meet at a specific point after passing through the lens.
- The real image can be projected onto a screen and is always inverted.
- The distance of the real image from the lens depends on the position of the object and the focal length of the lens. It can be either magnified or diminished.

Virtual Image:
- A virtual image is formed when the light rays appear to diverge after passing through the lens.
- The virtual image cannot be projected onto a screen and is always upright.
- The virtual image is formed on the same side as the object.

Concave Lens:
A concave lens is thinner at the center and thicker at the edges. It diverges or spreads out the light rays after refraction. The image formed by a concave lens is always virtual.

Virtual Image:
- The light rays passing through a concave lens appear to diverge.
- The virtual image formed by a concave lens is always upright and reduced in size.
- It is formed on the same side as the object.

Justification:
The nature of the image formed by a lens depends on the behavior of light rays after refraction. A convex lens brings the light rays together and can form a real or virtual image, depending on the position of the object and the lens. On the other hand, a concave lens diverges the light rays and always forms a virtual image. By observing the behavior of light rays, the orientation (inverted or upright) and the position (real or virtual) of the image can be determined. Thus, by analyzing the nature of the image formed, we can distinguish between a convex and a concave lens.