Final answer:
Objects with a negative focal length, in the context of optics, include diverging lenses and convex mirrors, which produce virtual images.
Step-by-step explanation:
According to the sign conventions used in optics, objects that have a negative focal length are those that cause light rays to diverge. Specifically, these are diverging lenses and convex mirrors. For a diverging lens, the focal length is negative (f = -1.0 cm) indicating that it forms a virtual, upright, and same-side image as the object. In the context of mirrors, a convex mirror also has a negative focal length, illustrating that parallel rays appear to diverge from a virtual focal point behind the mirror. The minus sign in the focal length indicates that the images formed are virtual, which is true for both diverging lenses and convex mirrors as per ray-tracing diagrams.