convex
Virtual, larger than object
concave mirror
Magnifying glasses use convex lenses
In case of concave lens the edges will be thicker compared to the central part. Whereas the convex lens has edges so thin compared to the central part. Concave lens would have only divergence effect. Parallel beam of light falling on one side of the concave lens after refraction would come out from the other side diverging out and so they appear to come from a point on the incident side of lens. So no real image is obtained. Thus the image will be a virtual image. If converging rays fall on the concave lens after refraction may be still converging but it convergence will be reduced a little bit and so instead forming a real image nearby the concave lens it will be formed somehow far away from the lens.
convex
Virtual, larger than object
A concave mirror would focus the light back towards the focal point of the mirror. You would not be able to use the mirror effectively with a concave.
a concave lens is thin in the middle, but thick on the sides. It does this: it makes what you look at bigger because it spreads out light
You would use a convex lens.
why do we use concave mirror as converging mirror
Concave
concave mirror
Concave lenses are used todiverge rays of light.
Magnifying glasses use convex lenses
The melon was so rotten that it became concave when it was pressed on.
a concave lense