According to cartesion sign convention, which mirror and which lens has negative focal length?

Name the mirror(s) that can give (i) an erect and enlarged image, (ii) same sized, inverted image

If an object is placed at the focus of a concave mirror, where is the image formed?

Why does a ray of light bend when it travels from one medium to another?

Concave mirrors are used by dentists to examine teeth. Why?