MCQ on Optical Microscope

The optical microscope, often known as the “light optical microscope,” is a kind of microscope that magnifies pictures of tiny materials using visible light and a lens system. Optical microscopes are the earliest kind of microscope, probably dating back to the 17th century in its current compound form. Although there are numerous complicated designs that strive to increase resolution and sample contrast, basic optical microscopes may be extremely simple. Optical microscopes have long been popular because they employ visible light, allowing materials to be seen directly with the naked eye.

1. Which component of the compound microscope aids in the collecting and focussing of light rays on the material to be examined?

a) Lens for the eyepiece

b) A lens that is objective

c) A lens with a condenser

c) The use of a magnifying lens

Answer- c

Explanation: A compound microscope is made up of three different lens systems. Between the light source and the specimen, the condenser lens captures and concentrates light rays in the plane of the microscopic field, allowing the specimen to be seen.

2. What is the shortest distance that the eye must go to concentrate on any object?

a) 11 cm

b) 25 cm

c) 32 cm

d) 42 cm

Answer- b

Explanation: The eye cannot concentrate on things that are brought closer to it than 25 cm; as a result, the maximum effective magnification distance is 25 cm. An item must also subtend a 1 degree or larger angle at the eye.

 3. A microscopes resolving power is a function of-

a) The wavelength of light that was employed

b) The lens system’s numerical aperture

c) Index of refraction

d) Light wavelength and numerical aperture of lens system

Answer- d 

Explanation: Resolving power refers to a microscope’s capacity to discern two nearby spots as distinct and independent. The numerical aperture (NA) of the lens system and the wavelength of light employed determine the resolving power. NA stands for the medium’s refractive index multiplied by the sine value of the half-aperture angle.

4. In light microscopy, the highest resolution is attained with-

a) The wavelength of visible light with the longest wavelength was selected 

b) A lens with a small numerical aperture.

c) Visible light with the shortest wavelength

d) The shortest visible light wavelength was chosen, as well as an objective with the highest numerical aperture.

Answer- d 

The link between numerical aperture (NA) and resolution is as follows:

wavelength / 2 = resolution (d) (NA)

As a result, the highest resolution is achieved by using the shortest wavelength of visible light and an objective with the highest NA.

5. The NA value of an oil immersion objective lens is___________.

a) 0.65

b) 0.85

c) 1.33

d) 1.00

Answer- c 

NA = refractive index * sine (explanation) (half-aperture angle).

Because the refractive index of air is 1, the maximum NA for a dry objective is less than 1.0. Because oil has a refractive index of 1.56, the NA values for oil immersion lenses are somewhat higher than 1.0 in the range of (1.2 to 1.4).

6. In fluorescence microscopy, which of the following controls the removal of all light except blue light?

a) Filter for exciters

b) Filtering barrier

c) Mirror made of dichroic glass

d) Arc light made of mercury

Answer- a 

The exciter filter removes all light except blue light in fluorescence microscopy; the barrier filter stops blue light but enables any other light generated by the fluorescing material to pass through and reach the eye.

7. _________ is used to acquire total magnification.

 a) The objective lens’ magnification power

b) The eyepiece’s magnification power

c) The condenser lens’ magnification power

d) Both the objective lens and the eyepiece have magnification power.

 Answer- d

Explanation: The total magnification is calculated by multiplying the objective’s magnifying power by the eyepiece’s magnifying power. Although eyepieces with greater or lower magnifications are available, most people use one with a magnification of 10X.

8. Prior to staining, which of the following is employed as a fixative in light microscopy?

a) Osmic acid

b) Glutaraldehyde

c) Heat

d) Osmic acid, glutaraldehyde, heat

Answer- c

Explanation: Because most staining procedures destroy cells, cells are sometimes stabilised before staining. Osmic acid and, in particular, glutaraldehyde is often used as chemical fixatives. However, heat is the most widely employed fixative in light microscopy.

9. The pace at which light passes through objects in phase contrast microscopy is-

a) Consistency

b) Their refractive indices are inversely proportional.

c) Their refractive indices are directly proportional to each other.

d) Their refractive indices are exponentially linked

Answer- b

The rate at which light goes through objects is inversely linked to their refractive indices, which is the basis for phase contrast microscopy. The phase of a light ray going through an item with a greater refractive index than the surrounding medium will be comparatively slowed because the frequency of light waves is independent of the medium through which they travel.

10. Which element of the light microscope is in charge of regulating the amount of light that enters the viewing area?

a) Coarse adjustment screw

b) Fine adjustment screw

c) Diaphragm

d) Condenser lens

Answer- c

Explanation: The diaphragm is a shutter-like mechanism attached on the condenser that opens and closes to let more or less light into the viewing region. The condenser lens simply aids in the condensing of light rays. For focusing under varied power lenses, coarse and fine adjustment screws are utilised.

11. A compound microscope’s magnification power is independent of 

a) the eye lens’ focal length and aperture

b) the objective lens’ apertures

c) the microscope’s tube length

d) none of the above.

Answer- b

12. The resolving power of a microscope is determined by-

a) The eye lens’ focal length and aperture 

b) The eye lens’ focal length and objective 

c) The objective and eye lens’ apertures 

d) The wavelength of light lighting the object

Answer- d