Question

A terrestrial telescope is made by introducing an erecting lens of focal length f between the objective and eye-piece lenses of an astronomical telescope. This causes the length of the telescope tube to increase by an amount equal to:       

Solution

Correct option is

4f

The minimum distance between the real object and real images is 4f.

SIMILAR QUESTIONS

Q1

A liquid is placed in a hollow prism of angle 60o. If angle of minimum deviation is 30o, what is the refractive index of the liquid?     

Q2

We have a right-angled isosceles prism. Its refracting index is 1.5. If a ray is incident normally on one of the two perpendicular surfaces which of the following phenomena will take place?    

Q3

A beam of light consisting of red, green and blue colours is incident on a right-angled prism. The refractive indices of the material of the prism for the above red, green and blue wavelengths are 1.39, 1.44 and 1.47 respectively. The prism will:

Q4

If the ratio of magnifications produced by a simple microscope in near point adjustment and far point adjustment is 6/5, then the focal length of the lens is (take D = 25 cm):    

Q5

When the length of a microscope increases its magnifying power:

Q6

The focal length of the objective and the eyepiece of a compound microscope are 1 cm and 5 cm respectively. An object is placed at a distance of 1.1 cm from the objective. If the final image is formed at the least distance of distinct vision, the magnifying power is:        

Q7

In a compound microscope the objective and eye-piece have focal lengths of 0.95 cm and 5 cm respectively, and are kept at a distance of 20 cm. The last image is formed at a distance of 25 cm from eye-piece. What is the total magnification of the microscope?       

Q8

A person cannot see objects clearly beyond 50 cm. The power of the lens to correct the vision is:

Q9

A presbyopic patient has near point as 30 cm and far point as 40 cm. The dioptric power for the corrective lens for seeing distant objects is:     

Q10

The length of a telescope is 36 cm. The focal lengths of its lenses can be