Tag: optical instruments : telescope

Questions Related to optical instruments : telescope

The focal length of the objective of an astronomical telescope is 1 m and it is in normal adjustment.Initially the telescope is focussed to a heavenly body. If the same telescope is to be focussed to an object at a distance of 21 m from the objective,then identify the correct choice

physics option c: imaging optical instruments : telescope the reflecting telescope optical telescope xx radio telescope and space telescopes

  1. eye piece should be displaced by 2 cm away from the objective

  2. eye piece should be displaced by 2 cm towards the objective

  3. eye piece should be displaced by 5 cm towards the objective

  4. eye piece should be displaced by 5 cm away from the objective

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Correct Option: D
Explanation:

We know, $ \dfrac {1}{f} = \dfrac {1}{v} - \dfrac {1} {u} $


We seeing heavenly body,  $u =  \infty$
$v = f = 1 m$

When seeing 21 m far
$u = - 21 m $
$f = 1 m$
$v = \dfrac {f u} {(f+u)} = 21 / 20 = 1.05 m$

So, eye piece need to move $1.05-1 = 0.05 m$ further away from objective

Answer. D) eye piece should be displaced by $5 cm$ away from the objective

The focal lengths of the objective and eyepiece of a telescope are 60cm and 5cm respectively.The telescope is focused on an object 360cm from the objective and the final image is formed at a distance of 30cm from the eye of the observer. The length of the telescope is

physics option c: imaging optical instruments : telescope the reflecting telescope optical telescope xx radio telescope and space telescopes

  1. 66.3 cm

  2. 86.3 cm

  3. 76.3 cm

  4. 96.3 cm

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Correct Option: C
Explanation:

$f _o = 60cm$


$f _e = 5cm$

$r _e = 30cm$

$L = ?$

$u _o = 360cm$

$\dfrac {1}{v _o} + \dfrac {1}{360} = \dfrac {-1}{60}$

$\dfrac {1}{v _o} = \dfrac {-1}{60} + \dfrac {1}{360}$

In which of the following instruments is the final image virtual?

physics observing space: telescopes optical instruments : telescope the reflecting telescope optical telescope xx radio telescope and space telescopes

  1. Projector

  2. Camera

  3. Microscope

  4. Telescope

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Correct Option: C,D
Explanation:

The final image of the camera and projector is real because it is obtained or projected on a screen or a photographic film or a chip.

A simple microscope uses convex lens and the object is placed between the focus and the optical center, so that, an erect, virtual and enlarged image of the object is formed.

A telescope uses two co-axially placed convex lenses in such a way that the focus of objective lens is past the focus of the eye piece. The first lens or the objective lens produces a real and inverted image of the object to be observed and this real image formed acts as an object for the eye piece convex lens and is between the focus and the optical center, so that, an inverted, virtual and enlarged image of the object is formed.

Hence, the correct answers are OPTIONS C and D.  

A planet is observed by an astronomical reflecting telescope having an objective of focal length $16 m$ and an eye-piece of focal length $2 cm$. Then :

physics option c: imaging optical instruments : telescope the reflecting telescope optical telescope xx radio telescope and space telescopes

  1. the distance between the objective and the eye - piece is $16.02 m$

  2. the angular magnification of the planet is $800$

  3. the image of planet is erect

  4. the objective is larger than eye - piece

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Correct Option: A,B,D
Explanation:

A telescope uses two co-axially placed convex lenses in such a way that the focus of objective lens is past the focus of the eye piece as evident here from the focal lengths of the objective lens and the eye piece. $ \therefore $ The objective lens is larger than eye piece.

Length of the tube is given as 
$ L = f _o + f _e = 16\ m + 2\ cm = 16.02\ m $

Angular magnification is given as:
$ m = \dfrac{f _o}{f _e} = \dfrac{1600}{2} = 800 $


Since, the first lens or the objective lens produces a real and inverted image of the object to be observed and this real image formed acts as an object for the eye piece convex lens and is between the focus and the optical center, so, an inverted, virtual and enlarged image of the object is formed. $ \therefore $ The final image is inverted. 

Hence, the correct answers are OPTIONS A,B and D.

An astronomical refracting telescope will have large angular magnification and high angular resolution, when it has an objective lens of

physics option c: imaging optical instruments : telescope the reflecting telescope optical telescope xx radio telescope and space telescopes

  1. large focal length and small diameter

  2. large focal length and large diameter

  3. small focal length and large diameter

  4. small focal length and small diameter

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Correct Option: B

Which of the following is not a fact about Hubble Telescope?

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  1. The Hubble Space Telescopes captures and transmits colorful images of objects in space such as dying stars and other galaxies.

  2. Although the Hubble Space Telescope can observe many things in space, it cannot observe the Sun or Mercury.

  3. The Hubble Space Telescope orbits about 353 miles above Earth

  4. None of the above

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Correct Option: D
Explanation:

All the facts mentioned about Hubble Telescope are true. The Hubble Telescope orbits 353 miles above earth and transmits colorful images of objects in space and through Hubble telescope we can observe many things in space except the sun or mercury.

Which of the following is not a part of HST?

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  1. Advanced Camera for Surveys (ACS).

  2. Faint Object Camera (FOC)

  3. Computer-controlled polishing machines

  4. Faint Object Spectrograph (FOS).

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Correct Option: C
Explanation:

Computer-controlled polishiing machines is not a part of HST. This is used mostly in fabrication purposes. In fabrication process automation techniques like computer-controlled polishing is used to achieve high level of fabrication.

DSN is a deep space network tracking station is 

physics universe and space science xx radio telescope and space telescopes launching vehicles optical instruments : telescope

  1. to track and communicate with interplanetary spacecraft missions.

  2. to track and provide the fuel to the spacecraft.

  3. to maintain the spacecraft

  4. none of the above

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Correct Option: A
Explanation:

DNS is a deep space network tracking station use to track and  communicate with interplanetary spacecraft missions, Along with tacking and communication DSN is also used to explore the furthest point of our solar system.

Which of the following is an early drawback of HST?

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  1. Its ground control system.

  2. Hubble failed to achieve a final sharp focus and the best image quality obtained was drastically lower.

  3. Images of point sources spread out over a radius of more than one arcsecond.

  4. All of the above

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Correct Option: B,C
Explanation:

As the early drawback of Hubble space telescope, Hubble filed to achieve a final sharp focus and the best image quality obtained was drastically lower. Also the image of point sources spread out over a radius of more than one arc second.

Which of the following is correct statement regarding HST?

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  1. The Hubble Space Telescope (HST) , has accurately determined the rate of expansion of the universe.

  2. Hubble has contributed to studies of the behavior of graphite composite structures in vacuum.

  3. Optical contamination from residual gas can also be observed from the HST.

  4. none of the above

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Correct Option: A,B,C
Explanation:

The hubble space Telescope (HST) has accurately determined rate of expansion of the universe. It has contributed to studies of the behaviour of graphite composite structures in vacuum and has observed the optical contamination from residual gases.