Question

According to the “New Cartesian Sign Convention” for mirrors, what sign has been given to the focal length of:

1. a concave mirror?
2. a convex mirror?

Answer 1

1. The sign given to the focal length of a concave mirror (according to the new cartesian sign convention) is negative. This is because the focus of a concave mirror is in front of the mirror, on the left side.
2. The sign given to the focal length of a convex mirror (according to the new cartesian sign convention) is positive. This is because the focus of a convex mirror is behind the mirror, on the right side.