No matter how far you stand from a mirror,your image appears erect. The mirror is likely to be

Define $1$ dioptre of power of a lens.

We wish to obtain an erect image of an object,using a concave mirror of focal length $15\, cm$. What should be the range of distance of the object from the mirror? What is the nature of the image? Is the image larger or smaller than the object? Draw a ray diagram to show the image formation in this case.

$A$ convex lens forms a real and inverted image of a needle at a distance of $50\, cm$ from it. Where is the needle placed in front of the convex lens if the image is equal to the size of the object? Also,find the power of the lens.

The image formed by a concave mirror is observed to be virtual,erect and larger than the object. Where should be the position of the object?

$A$ doctor has prescribed a corrective lens of power $+1.5\, D.$ Find the focal length of the lens. Is the prescribed lens diverging or converging?