Tag: physics

Questions Related to physics

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.

The sum of the focal lengths of the objective and an eyepiece, In case of an astronomical telescope is equal to : ( final image is at $\infty$)

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

  1. The length of the telescope

  2. Half the length of the telescope

  3. Double the length of the telescope

  4. None of these

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Correct Option: A
Explanation:

Answer is A.

The astronomical telescope makes use of two positive lenses: the objective, which forms the image of a distant object at its focal length, and the eyepiece, which acts as a simple magnifier with which to view the image formed by the objective. Its length is equal to the sum of the focal lengths of the objective and eyepiece, and its angular magnification is -fo/fe , giving an inverted image.
Hence, the sum of the focal lengths of the objective and an eyepiece, In case of an astronomical telescope is equal to the length of the telescope.

By which instrument we collect the space information:

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

  1. Convex lens

  2. Microscope

  3. Hubble Telescope

  4. None of these

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Correct Option: C
Explanation:

Hubble Telescope is a device used to collect space information.

The focal lengths of the objective and the eyepiece of an astronomical telescope are 20 cm and 5 cm respectively. If the final image is formed at a distance of 30 cm from the eyepiece, find the separation between the lenses required for distinct vision

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

  1. 32.4 cm

  2. 42.3 cm

  3. 24.3 cm

  4. 30.24 cm

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Correct Option: C
Explanation:

$f _{0}=20cm$


$f _{e}=5cm$

$V _{e}=30cm = D$

$L=?$

$L _{D}=f _{0}+ \dfrac{Df _e}{D+f _e}$ $=20+\dfrac{5\times 30}{35}=24.3 cm$

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