Explain the numerical aperture, Biology

Assignment Help:

Explain the Numerical Aperture?

Numerical aperture is a characteristic of each lens and is printed on the lens. It can be defined as a function of the diameter of the objective lens in relation to its focal length. It depends on the refractive index (η) of the medium in which the lens works and also upon the objective itself. Theta (φ) is defined as half of the angle of the cone of light entering an objective. Sin φ cannot be more than 1. Therefore, the lens working in air with refractive index 1 can have N.A.1. η will have to be increased for increasing the resolution. This can be done by using the mineral oil. Wavelength is also an important factor in resolution. With shorter wavelength, the resolving power increases. Just like magnification, resolution also has a limit. By decreasing wavelength, resolving power of the lens cannot be increased indefinitely because -

(a) the visible portion of the electromagnetic spectrum is very narrow and borders of very short wavelengths are found in ultraviolet range of spectrum.

(b) This relationship of Resolving Power with λ is valid only when light rays are parallel. As such 'Resolving Power' is also dependent on another factor, i.e., refractive index. When the light passes from air to glass slide, and from glass slide to air, there is a loss of light due to bending of rays. This reduces the numerical aperture and thus the resolving power of the lens. This loss in light can be compensated by using mineral oil in between glass slide and objective lens. Mineral oil is a colourless liquid having same refractive index as glass. This does decrease the bending of ray so that more light rays enter the objective lens thus increasing the resolving power. Proper specimen illumination is also important in determining resolution.


Related Discussions:- Explain the numerical aperture

Define effect of nutrition on the immune system, Define Effect of Nutrition...

Define Effect of Nutrition on the Immune System? Nutrition has a strong influence on the immune system of the elderly. Ageing induces dysregulation of the immune system, mainly

Approach grafting, Approach grafting In this method both scion and s...

Approach grafting In this method both scion and stock remain rooted. A small slice is cut off from the stem of scion and stock. Scion is bent towards the stock. The two c

The transport system in earthworm., The transport system in earthworm ...

The transport system in earthworm The scientific name of earthworm is megascolex. It consists of hearts, blood vessel and blood. There are 8 pairs of hearts in the earthw

Admission to the hospital - nursing, Admission to  the Hospital The ...

Admission to  the Hospital The  philosophy of  childcare, whether in the home, hospital, or  other community agency, should be consistently one of concern and support for the

Causes of reduced serum hdl levels, Q. Causes of reduced Serum HDL levels? ...

Q. Causes of reduced Serum HDL levels? Possible causes of reduced Serum HDL levels: - Cigarette smoking - Hypertriglyceridemia - Obesity - Genetic factors - Lack

Define vitamin and mineral supplements for treatment for pem, Define Vitami...

Define Vitamin and mineral supplements for treatment for PEM? All cases of severe PEM require multivitamin preparation to meet the increased demands during recovery. Iron (60 m

Calculate the number of grams of kmno4, How do i use the factor-label metho...

How do i use the factor-label method to calculate the number of grams of KMnO4 that you would need to make 100 ml of a 0.0045 M potassium permanganate solution? Be sure to show all

Children with infective endocarditis, Among neonates, IE typically involves...

Among neonates, IE typically involves the tricuspid valve of structurally normal hearts and is associated with very high mortality rates.  It is likely that many of these episodes

How many chromosomes and dna molecules found per cell, A cell in G1 of inte...

A cell in G1 of interphase has 12 chromosomes. How many chromosomes and DNA molecules will be found per cell when this original cell progresses to the G2?

Structure into which follicle is transformed after ovulation, Q. What is th...

Q. What is the structure into which the follicle is transformed after ovulation? What is the importance of that structure in the menstrual cycle? The follicle that released the

Write Your Message!

Captcha
Free Assignment Quote

Assured A++ Grade

Get guaranteed satisfaction & time on delivery in every assignment order you paid with us! We ensure premium quality solution document along with free turntin report!

All rights reserved! Copyrights ©2019-2020 ExpertsMind IT Educational Pvt Ltd