Microscopy - Quiz for SYBSC paper - III

Which part of the compound microscope helps in gathering and focusing light rays on the specimen to be viewed?

• Eyepiece lens

• Objective lens

• Condenser lens

• Magnifying lens

Answer explanation

Compound microscope contains three separate lens systems. The condenser lens is placed between the light source and the specimen and it gathers and focuses the light rays in the plane of the microscopic field to view the specimen.

What is the minimum distance for the eye to focus any object?

• 11 cm

• 25 cm

• 32 cm

• 4 2 cm

Answer explanation

The eye cannot focus on objects brought closer to it less than 25 cm; this is, accordingly the distance of maximal effective magnification. An object must also subtend an angle at the eye of 1 degree or greater.

Resolving power of a microscope is a function of ____________

• Wavelength of light used

• Numerical aperture of lens system

• Refractive index

• Wavelength of light used and numerical aperture of lens system

Answer explanation

The ability of a microscope to distinguish two adjacent points as distinct and separate is known as resolving power. Resolving power is a function of wavelength of light used and the numerical aperture (NA) of the lens system. NA refers to the refractive index of the medium multiplied with the sine value of the half-aperture angle.

The greatest resolution in light microscopy can be obtained with ___________

• Longest wavelength of visible light used

• An objective with minimum numerical aperture

• Shortest wavelength of visible light used

• Shortest wavelength of visible light used and an objective with the maximum numerical aperture

Answer explanation

Explanation: The relationship between numerical aperture (NA) and resolution is:-
Resolution (d) = wavelength / 2(NA)
Thus maximum resolution is obtained with the shortest wavelength of visible light and an objective with the maximum NA.

Oil immersion objective lens has an NA value of____________

• 0.65

• 0.85

• 1.33

• 1.00

Answer explanation

NA = refractive index * sine (half-aperture angle).
The maximum NA for a dry objective is less than 1.0 as the refractive index of air is 1. The values of NA for oil immersion lens is slightly greater than 1.0 in the range of (1.2 to 1.4) as the refractive index of oil is 1.56.

Total Magnification is obtained by __________

• Magnifying power of the objective lens

• Magnifying power of eyepiece

• Magnifying power of condenser lens

• Magnifying power of both the objective lens and eyepiece

Answer explanation

The total magnification is determined by multiplying the magnifying power of the objective by that of the eyepiece. Generally, an eyepiece having a magnification of 10X is used although eyepieces of higher or lower magnifications are available.

Which part of the light microscope controls the intensity of light entering the viewing area?

• Coarse adjustment screw

• Fine adjustment screw

• Diaphragm

• Condenser lens

Answer explanation

On the condenser is mounted a shutter like an apparatus called the diaphragm which opens and closes to permit more or less light into the viewing area. Condenser lens just helps in condensing the light rays. Coarse and fine adjustment screws are used for focusing under different power lens.