Final answer:
For a concave mirror with a focal length of 20 cm, the radius of curvature is 40 cm. If one wishes to place an object at the mirror's focal point with a focal length of 40 cm, the radius of curvature becomes 80 cm.
Step-by-step explanation:
The relationship between the focal length (f) of a concave mirror and its radius of curvature (R) is given by R = 2f. For a concave mirror with a given focal length of 20 cm, the radius of curvature would be R = 2 × 20 cm, which equals 40 cm. This relationship holds because the focal point is defined as the point where parallel rays of light either converge (in a concave mirror) or appear to diverge from (in a convex mirror), and it is located at half the distance of the radius of curvature from the mirror's surface.
In the specific example where it's desired to place the fluid-carrying pipe at the mirror's focal point, if the focal length is given as 40.0 cm, then the radius of curvature of the mirror would be R = 2f = 2 × 40.0 cm = 80.0 cm.