what did convex and concave len's image look like and why???

Answer 1

I like the phrasing "what did (...) look like"

Like you were supposed to have actually done some hard work, such as looking at something.

Answer 2

It helps to understand what lenses do to the light rays, and to trace them back from your eye to each lens.

Since some people may not understand the terms "convex" and "concave." I'll call them "fat" (in the centre) and "thin" (in the centre).

Think of a cross-section through each kind of lens.

Now let's draw an analogy with a simple prism with an angle, maybe 20 - 40 or so degrees at the vertex or "pointy end." When light approaches such a prism from one side, it always ends up emerging "bent away" from the vertex, and for this range of vertex angles, the bigger the vertex angle is, the greater the deviation away from the vertex.

The cross-section of each basic kind of lens can be thought of as being simply made up by "stacks" of appropriate parts of such prisms, the contributing prisms changing as one moves away from the axis of the lens.

In a "fat" lens, the local "prism bits" are from prisms that are made up by local prism bits that are "upright" or RIGHT WAY UP (vertex upwards) above the axis, and whose local "prism angle" increases upwards, away from that axis. Consequently, the further away from the axis that the rays of (say) parallel light enter the "fat" lens, the more those rays bend, so that all of them converge towards the axis.

This convergence of the rays means that, as far as a nearby eye is concerned, instead of coming in "parallel" (with a small angular cross-section) from a distant object, they're entering from a wider angle now. That means things look "enlarged." That's the principle of the "magnifying glass."

There are complications as the eye backs further away. Because of the converging rays, while the "image" is "real," and on the nearby side of the lens, there's a confusing region where things become very blurry. Beyond that, what you see are so-called "inverted images" (a misnomer, in fact). In telescopes an additional "fat" lens is introduced both to enlarge such an image again and "turn the image the right way up once more" (another misnome). But what I've described is the initial essence of what happens.

Conversely, in a "thin" lens, it's the other way round. Above the axis, the "locally stacked parts of the prisms" are all UPSIDE DOWN (vertex downwards), with THEIR angles also increasing away from the axis. This means that the rays emerging after the input of parallel rays diverge, more and more, as the entering point moves further away from the axis. Consequently, the eyes receive rays that are diverging from the lens. In effect one "sees" an "imaginary image" that is SMALLER, and somewhere on the other side of the lens, because that's where the rays appear to be diverging from. So such an image appears SMALLER than the original.

All this is from years of playing with lenses as a young, near-sighted schoolboy, plus what I picked up in my own high school in England. I give an accessible reference below.

Live long and prosper.

Answer 3

Can't splain it in scientific term's but, CONVEX is like the inside of a saucer, CONCAVE, is like the bottom of the saucer, The convex expands what you see,concave concentrates the image. It makes things appear smaller