What is the magnification of an astronomical telescope whose objective lens has a focal length of 82 cm, and whose eyepiece has a focal length of 2.8 cm?
Correct option is C. $$29X$$
The negative ratio of focal length of the objective to the focal length of the eyepiece give the focal length of the telescope
$$M=-\dfrac{f_0}{f_{e}}$$
Here, $$f_0$$ is focal length, M is magnification and $$f_e$$ is eyepiece of focal length
Substitute $$2.8$$ cm for $$f_{e}$$, and $$82cm$$ for $$f_0$$
$$M=-\dfrac{82}{2.8}=-29X$$