Which of the following is not true for a spherical concave mirror? a. it cannot produce virtual images
b. its focal length is half its radius
c. its focal length is positive
d. it can produce upright images

Its focal length is positive

Explanation:

A concave mirror is shown in attached figure. The distance from the pole to the focus of the mirror is called its focal length. Spherical mirrors are a part of a sphere.

As per conventions, we know that the axis opposite to x axis is taken as negative.

So, it is clear that the focal length of spherical concave mirror is negative.

Hence, the incorrect option is (c) " its focal length is positive".

a.   mass number from atomic number