Question

For a real object placed to the left of a spherical refracting surface, the object distance u is:

Options

• Usually positive, since the object faces the incident light

• Usually negative, as measured opposite to the direction of incident light

• Equal to the radius of curvature R

• Always zero, since the object lies on the pole

Answer 1

The object distance u is usually negative for a real object placed to the left of the surface, because distances measured opposite to the direction of incident light are taken as negative. This is the typical case encountered in most board numericals.