If the tube length of an astronomical telescope is $96 \ cm$ and the magnifying power is $15$ for normal setting,then the focal length of the objective is . . . . . . $cm$.

The focal length of the objective and eyepiece of a telescope are respectively $60 \, cm$ and $10 \, cm$. The magnitude of the magnifying power when the image is formed at infinity is:

The focal length of an objective of a telescope is $3 \ m$ and its diameter is $15 \ cm$. Assuming that for a normal eye,the diameter of the pupil is $3 \ mm$ for its complete use,the focal length of the eyepiece must be: (in $cm$)

Four convergent lenses have focal lengths $100 \, cm, 10 \, cm, 4 \, cm$ and $0.3 \, cm$. For a telescope with maximum possible magnification,we choose the lenses of focal length

To produce a magnified erect image of a far object,along with a convex lens,we will require:

When the tube length of an astronomical telescope is increased,its magnifying power will .......