Question

where is the image formed when the object is at focus of concave mirror​

Answer 1

When the object is at principal focus , the image is formed at infinity .

Image in attachment .

$\huge\underline{\texttt{EXPLANATION:}}$

→ The object is placed on the focus .

→ The first ray will pass parallel to the principal axis.

→ Then the ray will pass right through the focus .

→ The second ray will get totally reflected back .

→ The second ray will pass through the centre of curvature .

→ The first and second rays are parallel .

→ Hence the image will extend to infinity as the rays will never meet .