Chap#10 Optical Instruments

Question 1

A fly is sitting on the objective of a telescope pointed towards the moon. What effect is expected on the photography of the moon taken through the telescope?

Answer 1

There is a reduction in the intensity of the image

Question 2

A converging lens is used to form an image on a screen. When the upper half of the lens is covered by an opaque screen

Answer 2

Intensity of the image will decrease

Question 3

When the length of a microscope tube increases, its magnifying power:

Answer 3

Increases

Question 4

An object is placed at a distance of f/2 from a convex lens. The image will be:

Answer 4

At one of the foci, virutal and double its size

Question 5

A lens behaves as a converging lens in air and a diverging lens in water. The refractive index of the material is:

Answer 5

Between unity and 1.33

Question 6

A planet is observed by an astronomical refracting telescope having an objective of focal length 16m and an eyepiece of focal length 2 cm.

Answer 6

The image of the planet is inverted

Question 7

If tube length of astronomical telescope is 105 cm and magnifying power is 20 for normal setting, calculate the focal length of objective

Answer 7

100 cm

Question 8

To increase the magnification of a telescope:

Answer 8

The objective lens should be of large focal length and eyepiece should be of short focal length

Question 9

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

Answer 9

30 cm, 6 cm

Question 10

All of the following statements are correct except:

Answer 10

➡The total focal length of an astronomical telescope is the sum of the focal lengths of its two lenses.❌
➡The image formed by the astronomical telescope is always erect because the effect of the combination of the two lenses is divergent✅
➡The magnification of an astronomical telescope can be increased by decreasing the focal length of the eyepiece.❌