Tag: observing space: telescopes

Questions Related to observing space: telescopes

An astronomical telescope and a Galilean telescope use identical objective lenses. They have the same magnification, when both are in normal adjustment. The eyepiece of the astronomical telescope has a focal length f.

physics observing space: telescopes space research and satellites space travel space exploration and forms of light

  1. The tube length of the two telescope differ by f.

  2. The tube length of the two telescopes differ by 2f.

  3. The Galileans telescope has shorter tube length.

  4. The Galileans telescope has longer tube length.

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Correct Option: B,C
Explanation:

In normal adjustment, tube length of an astronomical telescope is $ \left( { f } _{ 0 }+{ f } _{ e } \right) $ and that of Galilean telescope is $ \left( { f } _{ 0 }+{ f } _{ e } \right) $, where $ { f } _{ 0 }$ and $ { f } _{ e }$ are the focal lengths of the objective and the eyepiece respectively. 


$ Here,\quad { f } _{ e }=f$

magnification  =$ \dfrac { { f } _{ 0 } }{ { f } _{ e } } $ for both telescope.

A terrestrial telescope is made by introducing an erecting lens of focal length, $f$, between the objective and eyepiece lens of an astronomical telescope. This causes the length of telescope tube to increase by an amount equal to

physics observing space: telescopes space research and satellites space travel space exploration and forms of light

  1. $f$

  2. $2f$

  3. $3f$

  4. $4f$

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Correct Option: D
Explanation:

Since, the mInimum distance between the real object and real image is $4f$. 

Therefore length of telescope increase by $4f$.

The objective of a telescope has a focal length of $1.2\ m$. It is used to view a $10.0\ m$ tall tower $2\ km$ away. What is the height of the image of the tower formed by the objective.

physics observing space: telescopes space research and satellites space travel space exploration and forms of light

  1. $2\ mm$

  2. $4\ mm$

  3. $6\ mm$

  4. $8\ mm$

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Correct Option: A

In an astronomical telescope, the distance between the objective and the eyepiece is 36 cm and the final image is formed at infinity. The focal length $f _0$ of the objective and the focal length $f _e$ of the eyepiece are

physics observing space: telescopes space research and satellites space travel space exploration and forms of light

  1. $f _0=45 cm$ and $f _e=-9 cm$

  2. $f _0=50 cm$ and $f _e=22 cm$

  3. $f _0=65 cm$ and $f _e=7 cm$

  4. $f _0=30 cm$ and $f _e=6 cm$

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Correct Option: A,D
Explanation:

The focal lengths be $f _{o}$ and $f _{e}$ 


then $f _{o}+f _{e}=36$ for the image to be at infinity 

option $A$ is correct as $45-9=36$

The device used to observe stars and other heavenly bodies is

physics observing space: telescopes space research and satellites space travel space exploration and forms of light

  1. periscope

  2. microscope

  3. telescope

  4. compound microscope

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Correct Option: C
Explanation:

A telescope is an optical instrument designed to make distant objects like stars, planets, appear nearer, containing an arrangement of lenses, or of curved mirrors and lenses, by which rays of light are collected and focused and the resulting image magnified.

A telescope gives an .............. (inverted / erect) and ........ (enlarged/diminished) image of a distant object. Choose the correct alternative.

physics observing space: telescopes space research and satellites space travel space exploration and forms of light

  1. Inverted, diminished

  2. Inverted, enlarged

  3. Erect, diminished

  4. Erect, enlarged

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Correct Option: A
Explanation:
Telescopes are  used to obtain an enlarged image of a distant object, it uses a curved lens or mirror to collect light from distant objects and to focus that light on an image and creates a brighter and sharper image. The focused image formed by the objective lens of a telescope is magnified by a smaller second lens called an eyepiece.

State whether true or false :

Both the telescope and compound microscope make use of two lenses-one concave and one convex.

physics observing space: telescopes space research and satellites space travel space exploration and forms of light

  1. True

  2. False

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Correct Option: B
Explanation:

Both the telescope and compound microscope make use of two lenses–one concave and one convex. [a] false

Both the lenses are convex lenses

The main difference between telescope and microscope is that microscopes are used to magnify small objects that are at a short distance from the viewer whereas telescopes are used to magnify large objects that are at a large distance from the viewer. In refracting telescopes, there are typically two convex lenses. One lens acts as the objective lens: this lens gathers light from faraway objects and forms a real, inverted image of the object at its focal point. A second lens, called the eyepiece

Microscopes are used to look at magnified images of small objects. A simple microscope consists of a single convex lens. The lens is held close to the object so that the object is between the lens and its focal point.

A simple telescope has

physics observing space: telescopes space research and satellites space travel space exploration and forms of light

  1. A convex lens and a concave lens

  2. A concave mirror and a convex lens

  3. Two convex lenses

  4. Two concave lenses

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Correct Option: C
Explanation:

A simple telescope consist of two convex lenses 

1. objective lens - large focal length
2. eyepiece - small focal length
$\therefore$ Option C is correct.

Match List-I with List- II and select the answer using the codes given below the lists:

List-I List-II
A. Microscope 1. To see objects on the surface by an observer in a trench
B. Telescope 2. To see small objects
C. Periscope 3. To see distant objects
D. Camera 4. To take photographs of objects
physics observing space: telescopes space research and satellites space travel space exploration and forms of light

  1. $2\, \quad\, 1\, \quad\, 4\, \quad\, 3$

  2. $1\, \quad\, 2\, \quad\, 3\, \quad\, 4$

  3. $2\, \quad\, 3\, \quad\, 4\, \quad\, 1$

  4. $2\, \quad\, 3\, \quad\, 1\, \quad\, 4$

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Correct Option: D
Explanation:

Microscope - is used to see small object which cannot be seen by naked eye

telescope - is used to see object which are situated at a long distance eg. sun, moon , planet
periscope -The uses of a periscope include observation around barriers and at times when viewing a location directly would be dangerous. Periscopes are typically used in submarines to see above the water.
Camera - is used to capture photos of objects.

Thus matching will be
A - 2 , B - 3   C - 1  and  D - 4

 hence Option D is correct.

The focal length of eye lens and object lens of a telescope is 4 mm and 4 cm respectively. If final image of an far object is at $\displaystyle \infty $. Then the magnifying power and length of the tube are:

physics observing space: telescopes space research and satellites space travel space exploration and forms of light

  1. 10, 4.4 cm

  2. 4, 44 cm

  3. 44, 10 cm

  4. 10, 44 cm

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Correct Option: A
Explanation:

Magnification is the amount that a telescope enlarges its subject. Its equal to the telescopes focal length divided by the eyepieces focal length. As a rule of thumb, a telescopes maximum useful magnification is 50 times its aperture in inches (or twice its aperture in millimeters). 
That is, $M = fo / fe$
In this case, the focal length of eye lens and object lens of a telescope is 4 mm = 0.4 cm and 4 cm respectively.
So, Magnification $M = fo / fe = 4 / 0.4 = 10.$
Focal length of the eyepiece is the distance from the center of the eyepiece lens to the point at which light passing through the lens is brought to a focus.
Focal length of the objective is the distance from the center of the objective lens (or mirror) to the point at which incoming light is brought to a focus.
The length of the tube is given as sum of the focal lengths of the eye lens and the object lens.
So, Length of the tube $ = fo + fe = 4 + 0.4 = 4.4 cm.$
Hence, the magnifying power and length of the tube are: 10, 4.4 cm.