Tag: observing space: telescopes

Questions Related to observing space: telescopes

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

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

Show answer
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.

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.  

Choose the correct answer from the alternatives given.
Maxwell in his famouse questions of  eletromagnetism introduce the concept of:

the nature of electromagnetic waves space exploration and forms of light observing space: telescopes electromagnetic waves physics

  1. ac current

  2. displacement current

  3. impedance

  4. reatance

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Correct Option: B
Explanation:

Maxwell in his famous question's of electromagnetism introduce the concept of displacement current

$J=J _E+J _C\ \quad=\epsilon _0\cfrac{dE}{dT}+\cfrac{dP}{dT}$

Which of the following has/have zero average value in a plane electromagnetic wave?

the nature of electromagnetic waves space exploration and forms of light observing space: telescopes electromagnetic waves physics

  1. Both magnetic and electric fields

  2. Electric fields only

  3. Magnetic field only

  4. None of these

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Correct Option: A
Explanation:

Both electric and magnetic field have sinusoidal nature in a plane electromagnetic wave. As we know, the average value of a sinusoidal wave is zero, so both magnetic and electric fields have average values zero.

Which of the following ray is not electromagnetic wave?

the nature of electromagnetic waves space exploration and forms of light observing space: telescopes electromagnetic waves physics

  1. X-rays

  2. $\gamma$-rays

  3. $\beta$-rays

  4. Heat rays

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Correct Option: C
Explanation:

Cosmic rays, γ-rays, and X-rays are part of electromagnetic spectrum, while β-rays are emitted by radioactive elements. Hence β-rays is not electromagnetic waves.

Which of the following is not true for electromagnetic waves?

the nature of electromagnetic waves space exploration and forms of light observing space: telescopes electromagnetic waves physics

  1. They transport energy.

  2. They have momentum.

  3. They travel at different speeds in air depending on their frequency.

  4. They travel at different speeds in medium depending on their frequency.

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Correct Option: C
Explanation:

Electromagnetic wave have constant velocity in a particular medium and it is independant of frequency and it is equal to $V=\sqrt{\dfrac{1}{\mu _0 \epsilon _0}}=3 \times 10^8 \ m/s$ 

Option C