Q1.
How can we distinguish between concave and convex mirrors?
Answer
There are three quick tests, and they check three different things.
| Test | Concave mirror | Convex mirror |
|---|---|---|
| Side view (Activity 10.2) | Shiny surface hollowed inwards | Shiny surface bulges outwards |
| Image of an object held close | Erect and enlarged | Erect and diminished |
| Object moved far away | Image becomes inverted | Image stays erect, only shrinks |
| A parallel beam of light on it | Reflected beam converges | Reflected beam diverges |
Why the image test is the surest one: the shape test can fail if the curvature is very gentle, but the image test uses the effect of that curvature, which is easy to see. And the beam test goes to the root of it: converging or diverging is the one property that follows directly from whether the surface curves in or out.
Tip: a plane mirror gives the third answer — the image stays the same size at every distance, and a parallel beam stays parallel.