Tag: diffraction

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Questions Related to diffraction

Multiple choice physics wave optics resolving power of optical instruments resolution of optical instruments diffraction

In an astronomical microscope, the focal length of the objective is made :

  1. shorter than that of the eye piece

  2. greater than that of the eye piece

  3. half of the eye piece

  4. equal to that of the eye piece
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

In an Astronomical telescope, the objective lens has a greater radius than the eyepiece.

Thus the objective lens has a greater focal length than the eyepiece.

Option B is correct.

Multiple choice physics wave optics resolving power of optical instruments resolution of optical instruments diffraction

If the apertature of a telescope is decreased the resolving power will

  1. increases

  2. decreases

  3. remain same

  4. zero
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Resolving power of a telescope=$\dfrac{a}{1.22\lambda}$

where $a$ is the aperture of the telescope.
Thus resolving power$\propto $ aperture.
Hence, if the aperture of telescope decreases, the resolving power decreases.

Multiple choice physics wave optics resolving power of optical instruments resolution of optical instruments diffraction

The resolving power of a telescope depends on :

  1. length of telescope

  2. focal length of objective

  3. diameter of the objective

  4. focal length of eyepiece
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Resolving power of telescope $R=\dfrac{1}{\Delta \theta}=\dfrac{a}{1.22 \lambda}$
where, $\Delta \theta$ is angular separation between two objects.
            $a$ is the diameter of the objective.
            $\lambda$ is wavelength of light.
So, clearly resolving power of a telescope depends on diameter of the objective.

Multiple choice physics wave optics resolving power of optical instruments resolution of optical instruments diffraction

The diameter of the objective of a telescope is $a$, its magnifying power is $m$ and wavelength of light $\lambda $ . The resolving power of the telescope is :

  1. $\dfrac{(1.22\lambda )}{a}$
  2. $\dfrac{1.22a}{\lambda} $
  3. $\lambda (1.22a)$
  4. $\dfrac {a} {1.22\lambda} $
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Resolving power of telescope:
$R=\dfrac{1}{ \theta}=\dfrac{a}{1.22 \lambda}$


where $\theta$ is angular resolution, a is diameter of the objective and $\lambda$ is wavelength of light.

Multiple choice physics wave optics resolving power of optical instruments resolution of optical instruments diffraction

The resolving power of human eye is :

  1. $\approx 1'$
  2. $\approx 1^{0}$
  3. $\approx 10"$
  4. $\approx 5"$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The normal pupil size of a human eye is 4 mm.which sets a minimum resolution approximately 1' to 2'.we want to pull small objects as close to our eyes as possible to be able to see them, but there is a minimum distance of comfortable viewing which is roughly at 25 cm. Hence, correct option is A.

Multiple choice physics wave optics resolving power of optical instruments resolution of optical instruments diffraction

An electron microscope is superior to an optical microscope in terms of:

  1. having better resolving power

  2. being easy to handle

  3. low cost

  4. quickness of observation
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The biggest advantage of an electron microscope over optical microscope is that they have a higher resolution and are therefore capable of a higher magnification ( up to $2 \ million$ times ). 

However, optical microscopes show a useful magnification up to $1000-2000 $ times. This is a limit imposed by the wavelength of light. Electron microscopes, therefore, allow for the visualization of structures that would normally be not visible by optical microscopy.

Multiple choice physics wave optics resolving power of optical instruments resolution of optical instruments diffraction

Assertion : Resolving power of a telescope is more if the diameter of the objective lens is more.
Reason : Objective lens of large diameter collects more light

  1. Both Assertion and Reason are correct and Reason is correct explanation of Assertion

  2. Assertion and Reason both are correct but Reason is not correct explanation of Assertion.

  3. Assertion is true but Reason is false.

  4. Both Assertion and Reason are false.
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Resolving power of a telescope is more if the diameter of the objective lens is more because $R=\dfrac{a}{1.22 \lambda}$
where, a is diameter of the objective. objective lens of large diameter collects more light but does not increase the resolving power of the telescope because resolving power increases when angular separation increases.

Multiple choice physics wave optics resolving power of optical instruments resolution of optical instruments diffraction

Resolving power of a telescope increases with :

  1. increase in focal length of eyepiece

  2. increase in focal length of objective

  3. increase in aperture of eyepiece

  4. increase in aperture of objective
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Resolving power of a telescope:
$R=\dfrac{a}{1.22 \lambda}$
where, $a$ is diameter of the objective
so, $R$ increases when a is increased and $a$  increases when aperture of objective is increased