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Four lenses of focal length $+15cm,+20cm,+150cm$ and $+250cm$ are available for making an astronomical telescope. To produce the largest magnification, the focal length of the eyepiece should be

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

  1. $+15cm$

  2. $+20cm$

  3. $+150cm$

  4. $+250cm$

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Correct Option: A
Explanation:

In astronomical telescope, magnification is inversely proportional to focal length of eye piece. Hence, it will be minimum i.e. +15cm as in question.

A reflecting telescope utilises :

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

  1. a convex mirror

  2. a concave mirror

  3. a prism

  4. a plano-concave lens

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Correct Option: B
Explanation:

Unlike convex mirrors, concave mirrors show different image types depending on the distance between the object and the mirror. That is why a reflecting telescope utilizes a concave mirror. If you observe the design of a reflecting telescope, it uses the incoming rays to focus through a concave mirror to focus on the second mirror which in turn sends the rays to the eye-piece. So, the concave mirror is intrinsic to the design of a reflecting telescope.

This question has Statement-1 and Statement-2. Of the four choices given after the Statements, choose the one that best describes the two Statements.
Statement 1 : Very large size telescopes are reflecting telescopes instead of refracting telescopes.
Statement 2 : It is easier to provide mechanical support to large size mirrors than large size lenses.

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

  1. Statement-1 is true and Statement-1 is false and statement-2 is true

  2. Statement-1 is false and Statement-2 is true

  3. Statements-1 and Statement-2 are true and Statement-2 is correct explanation for Statement-1

  4. Statements-1 and Statements-2 are true and Statement-2 is not the correct explanation for Statement-1

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Correct Option: C

In the spectrum of light from a star, the wavelength of a particular line is measured to be $4747 $, while the actual wavelength of the line is $4700 $. What is the relative velocity ?

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

  1. $2\times10^5 m/s$

  2. $3\times10^5 m/s$

  3. $3\times10^6 m/s$

  4. $4.5\times10^6 m/s$

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Correct Option: B

The objective of a telescope A has diameter 3 times that of the objective of telescope B, How much greater amount of light is gathered by A as compared to B?

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

  1. $\dfrac { 1 }{ 9 } $

  2. $\dfrac { 1 }{ 3 } $

  3. 3

  4. 9

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Correct Option: A

In telescope, ratio of resolving power due to light of $\lambda=400\mathring {A}$ and $\lambda =6000\mathring {A}$ is ______

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

  1. $4:5$

  2. $3:2$

  3. $2:3$

  4. $5:4$

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Correct Option: B

For an electron microscope, which of the following is false ?

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

  1. It uses magnetic lens to converge electron beam.

  2. Its resolving power is directly proportional to accelerating potential of electron.

  3. Its resolving power is inversely proportional to wavelength of electrons

  4. Magnification attained with the help of of it of the order of $10^6$.

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Correct Option: B

 If an object subtend angle of $2^o$ at eye when seen through telescope having objective and eyepiece of focal length $f = 60\, cm $and $f = 5\, cm$ respectively than angle subtend by image at eye piece will be 

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

  1. $16^o$

  2. $50^o$

  3. $10^o$

  4. $24^o$

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Correct Option: A

A telescope has an objective of focal length $50 cm$ and an eye-piece of focal length $5 m$ THe least distance of distinct vision is $25 cm$. The telescope is focused for distinct vission a scale $200 cm$ away from the objective.The separation between the two lenses is nearly 

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

  1. $71 cm$

  2. $61 cm$

  3. $81 cm$

  4. $51 cm$

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Correct Option: A

Match the items given in A, B, C and D against their corresponding description given in 1, 2, 3, 4 and 5.
A. Astronomical telescope
B. Galilean Telescope
C. Simple Microscope
D. Compound Microscope

1. Contains one convex lens
2. Contains one concave lens
3. Contains a convex lens of large focal length in the objective and a convex lens of small focal length in the eye-piece
4. Contains a convex lens of small focal length in the objective and a convex lens of large focal length in the eye-piece
5. Contains a convex lens of large focal length in the objective and a concave lens of small focal length in the eye-piece. 

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

  1. $2\, \quad\, 3\, \quad\, 1\, \quad\, 5$

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

  3. $2\, \quad\, 5\, \quad\, 3\, \quad\, 4$

  4. $3\, \quad\, 5\, \quad\, 1\, \quad\, 4$

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Correct Option: D
Explanation:

A). Astronomical telescope - Contains a convex lens of large focal length in the objective and a convex lens of small focal length in the eye-piece

B.) Galilean Telescope - Contains a convex lens of large focal length in the objective and a concave lens of small focal length in the eye-piece
C). Simple Microscope - Contains one convex lens
D.) Compound Microscope - Contains a convex lens of small focal length in the objective and a convex lens of large focal length in the eye-piece
Thus,
A  -  3 , B  -  5 , C  -  1 and D  -  4 , hence Option D is correct.