Of physics:
what is tension ? give full defination with explanation

Tension is the force supported by a cable, string or a rope. Say for example, you have a ball attached to a string, tied to your ceiling. The force with which the ball pulls the string down (that is, the force supported by the string) is the tension of the string.

 R= 1.6 m

Explanation:

The radius of curvature of mirror and focal length is given by

                   R=2f

           where R is the radius of curvature

                      f is the focal length

As the telephoto camera uses mirror instead of lens , we can calculate the radius of curvature of mirror which has focal length of 0.8m which is same as that of lens.

          The radius of curvature of mirror is R =2*0.8

                         R= 1.6 m