Opera glass have a minimum length of 20 cm and a magnifying power of 5 when viewing distant objects. The focal lengths of lenses used are

Q. An opera glass has a length of $30$ cm and its magnifying power is $5$ when used to view distant objects. Calculate the focal length of its lenses.

Q. A man with normal near point $25cm$ reads a book with small print using a magnifying glass, a thin convex lens of focal length $5cm$. The closest and farthest distances from the magnifying glass at which he can read the book when viewing through the magnifying glass, respectively are -

Q. A man with normal near point $\left(25cm\right)$ reads a book with small point using a magnifying glass, a thin convex lens of focal length $5cm$.

Q.

The magnifying power of a telescope is 9. When it is adjusted for parallel rays, the distance between the objective and eyepiece is found to be 20 cm. The focal lengths of lenses are:

Q. The length of the tube of a compound microscope $15cm$. The focal length of objective and eye lenses are 1 cm and $5cm$ respectively. The magnifying power of microscope for relaxed vision is: