Resolving Power of Telescope and Microscope - A Complete Guide

In this chapter, we will study about resolving power and learn more about resolving the power of Telescope and Microscope . We will study the resolving power of Grating, limit of resolution and resolving power of human Eye. In the last we will see the difference between telescope and microscope and study further in details about resolution limit, types of microscope and unit of numerical aperture.

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This Story also Contains

1. What is Resolving Power and Resolution in Physics
2. Difference between Telescope and microscope
3. Microscope
4. Telescope

What is Resolving Power and Resolution in Physics

1. When two point size object placed at minimum separation either linear or angular for which they appears just separated is known as limit of Resolution of an optical instrument
2. The reciprocal of limit of resolution of an optical aperture is known as Resolving Power

• Difference between resolution and magnification is that the former is distinct between two objects and later enlarges the objects.

The Rayleigh criterion for the minimum resolvable angle is

θmin = 1.22 λ/D

Where, D is the diameter of the aperture of the instrument

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Resolving Power of Grating

It is the capacity of an aperture to separate two different diffraction maxima formed by two different wavelengths which are very close to each other.

Resolving Power and its SI unit

Resolving Power of optical instruments is defined as the capacity of its to distinguish between smaller details .

For the objects to be distinguished kept at a smaller distance , resolving power should be higher.

SI unit of Resolving Power

Resolving power is dimensionless quantity and thus it has no SI unit

Note: Resolving Power is the ratio between mean wavelength of different spectral lines and difference of wavelength between them and as there is the same quantity having the same unit thus there is no SI unit.

Difference between Telescope and microscope

• A Telescope is an optical instrument which let us see object up close which is at distant from it like Planets , Stars etc. while
• A microscope is an optical instrument which also allows seeing objects up close but with detailed magnification. This instrument is used mainly to enlarge and magnify smaller objects like microorganisms , cells, study of plants etc.

Microscope

• Resolving power of Microscope/Resolving power of microscope formula
• The resolving power formula is given by:
  Resolving power = 1/ Difference in Distance(∆d) =2a / λ
  Where a is the numerical aperture and λ is the wavelength

Types of Microscope

• Light Microscope
• Compound microscope

Resolution of Electron Microscope

As we know Resolution depends upon wavelength and wavelength of electrons is much smaller than other particles so theoretically resolution of electron microscope comes to be unlimited.

Resolution of Compound Microscope

Restraints of resolution of simple Microscope can be removed by using Compound Microscope as it has two lens arrays namely objective lens and Eyepiece. The combination of these lens arrays results in formation of an enlarged virtual image.

Numerical Aperture Derivation

NA= √( Ƞ1^2- Ƞ2^2)

Where, Ƞ1 is refractive index of core

Ƞ2 is refractive index of cladding.

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Telescope

• Telescope is an optical instrument which consists of a lens , mirror or combination of both these to close up distant objects by means of absorption, reflection of electromagnetic radiation.

Types of telescope

On the basis of wavelength Telescope is distinguished as:

Optical Telescope

X-Ray Telescope

Ultraviolet Telescope

Telescope Resolution

It is an ability of a telescope to distinguish two point source objects into different images.

Principles of Telescope

We try to understand this by an example:

Let's say on a hazy night we were driving through the forest and were experiencing a lot of obstacles to see through the foggy light . We saw a beam of light coming towards us and we were unable to study the origin of point source or unable to distinguish the point source but as the object came closer by, we found it was a four wheeler instead of motorbike as we could easily see different point sources of light.

Same principle is followed by Telescope

Telescope Power

In simple term , Telescope power is its ability to enlarge its object size

Resolving power of Telescope formula is given by:

Resolving Power =D/d= a / 1.22 λ

Where D= distance of object from the lens of telescope

a= Resolution of two slit

How can we change Resolving Power

As we can see Resolving Power of a telescope depends on the resolution of two slits, so by increasing the value of (a) we can increase the power value.

Resolving Power of an Eye

Like telescopes or other optical instruments our Eyes also have resolving power. It depends on size of pupils ,as compared to diameter of aperture of other optical instruments our pupils size is comparatively very small hence it is obvious that resolving power of our Eyes is lower than all other optical instruments.

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NCERT Physics Notes:

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