
Define the resolving power of microscopes. Write its formula. How will it vary, when
(a) wavelength of incident light is decreased.
(b) the aperture of the objective lens is decreased.
Answer
512.4k+ views
Hint: Microscopes are used to see objects which are too small for naked eye. We use circular openings like lenses to magnify the object. Whenever we use a circular opening like a lens or iris of our eye. A circular diffraction pattern is formed. We need to differentiate between two such diffraction patterns which are very close to each other. The resolving power of a microscope gives us that limit.
Complete step by step solution:
Resolving power of microscopes is given by the inverse of the distance between two lines or points that can be resolved clearly using the microscope.
Let’s understand why we need this quantity. When we see an object through a circular opening it creates a diffraction pattern as shown in the following figure. The concentric rings are called Airy’s rings.
When two objects are very close to each other, we need to make sure that these rings do not overlap with each other and create a blurry image of the two objects. This gave rise to the Rayleigh criterion.
We can use this criterion to find the resolving power of microscopes. It is given by the inverse of the distance between two objects that can be resolved. Hence, we can write the Abbe’s criterion as,
Where,
is the resolving power of the microscope
is the refractive index separating the object and aperture.
is the wavelength of the light used for observation.
The term is also called Numerical Aperture (N.A.) of the microscope. Hence, we can write,
.................(1)
(a) From equation (1) we can say that the resolving power of the microscope will increase if the wavelength of incident light is decreased.
(b) From equation (1) we can again say that the resolving power of the microscope will decrease if we decrease the aperture of the objective lens.
Note: Rayleigh’s criterion is given by,
Where,
is the half angle subtended by the first minimum at the source
is the wavelength of light that is being used for measurement
is the distance between the two objects
This is an important criterion to observe two fully resolved objects using telescopes or microscopes.
Complete step by step solution:
Resolving power of microscopes is given by the inverse of the distance between two lines or points that can be resolved clearly using the microscope.
Let’s understand why we need this quantity. When we see an object through a circular opening it creates a diffraction pattern as shown in the following figure. The concentric rings are called Airy’s rings.

When two objects are very close to each other, we need to make sure that these rings do not overlap with each other and create a blurry image of the two objects. This gave rise to the Rayleigh criterion.
We can use this criterion to find the resolving power of microscopes. It is given by the inverse of the distance between two objects that can be resolved. Hence, we can write the Abbe’s criterion as,
Where,
The term
(a) From equation (1) we can say that the resolving power of the microscope will increase if the wavelength of incident light is decreased.
(b) From equation (1) we can again say that the resolving power of the microscope will decrease if we decrease the aperture of the objective lens.
Note: Rayleigh’s criterion is given by,
Where,
This is an important criterion to observe two fully resolved objects using telescopes or microscopes.
Latest Vedantu courses for you
Grade 11 Science PCM | CBSE | SCHOOL | English
CBSE (2025-26)
School Full course for CBSE students
₹41,848 per year
Recently Updated Pages
Master Class 12 Business Studies: Engaging Questions & Answers for Success

Master Class 12 English: Engaging Questions & Answers for Success

Master Class 12 Social Science: Engaging Questions & Answers for Success

Master Class 12 Chemistry: Engaging Questions & Answers for Success

Class 12 Question and Answer - Your Ultimate Solutions Guide

Master Class 11 Economics: Engaging Questions & Answers for Success

Trending doubts
Draw a labelled sketch of the human eye class 12 physics CBSE

a Tabulate the differences in the characteristics of class 12 chemistry CBSE

Which one of the following is a true fish A Jellyfish class 12 biology CBSE

Why is the cell called the structural and functional class 12 biology CBSE

Differentiate between homogeneous and heterogeneous class 12 chemistry CBSE

Write the difference between solid liquid and gas class 12 chemistry CBSE
