Physics
Physics
Problem
An object is placed at the principal focus F of a concave mirror. What is the nature and position of the image formed? a) Real, inverted, at the centre of curvature b) Virtual, erect, behind the mirror c) Real, inverted, at infinity d) Virtual, erect, atIntuitive explanation
When an object sits exactly at the focal point of a concave mirror, you're at a special boundary condition where the mirror's geometry breaks down the usual image-forming rules. The key insight is that rays from the object converge after reflecting, but they do so at infinity—meaning the reflected rays travel parallel to each other rather than meeting at a real point. This tells you something fundamental about both where the image appears and what kind of image it is.
Intuitive explanation
When an object sits exactly at the focal point of a concave mirror, you're at a special boundary condition where the mirror's geometry breaks down the usual image-forming rules. The key insight is that rays from the object converge after reflecting, but they do so at infinity—meaning the reflected rays travel parallel to each other rather than meeting at a real point. This tells you something fundamental about both where the image appears and what kind of image it is.