Q: The limit of resolution in a light microscope is mathematically described by which formula?

$$d = \frac{\lambda}{2n \sin \theta}$$

Q: If the objective lens of a microscope has a numerical aperture (NA) of 1.25 and the wavelength of light used is 500 nm, what is the theoretical limit of resolution? Use the formula $$d = \frac{\lambda}{2n \sin \theta}$$, where $$n \sin \theta = NA.$$

$$d = \frac{500}{2 \times 1.25} = 200 nm$$

Question 1

Which part of a compound light microscope is responsible for focusing the light onto the specimen?

Accepted Answer

Condenser

Question 2

The limit of resolution in a light microscope is mathematically described by which formula?

Accepted Answer

$$d = \frac{\lambda}{2n \sin 	heta}$$

Question 3

Which type of light microscope is best suited for visualizing unstained live bacterial cells?

Accepted Answer

Dark field

Question 4

A student wants to increase the resolution of their microscope image. Which of the following actions would be most effective?

Accepted Answer

Increase the angle of light collected by the objective lens

Question 5

Which property describes the degree to which light bends as it moves from one medium to another?

Accepted Answer

Refractive index

Question 6

Why are basic dyes commonly used to stain bacterial cells?

Accepted Answer

Bacterial cells have a slightly negative charge

Question 7

Which type of electron microscope is best for viewing the 3D exterior morphology of a specimen?

Accepted Answer

Scanning Electron Microscope (SEM)

Question 8

A microbiologist is using a phase contrast microscope. What is the main advantage of this type of microscope?

Accepted Answer

It enhances contrast of internal structures in unstained cells

Question 9

If the objective lens of a microscope has a numerical aperture (NA) of 1.25 and the wavelength of light used is 500 nm, what is the theoretical limit of resolution? Use the formula $$d = \frac{\lambda}{2n \sin 	heta}$$, where $$n \sin 	heta = NA.$$

Accepted Answer

$$d = \frac{500}{2 	imes 1.25} = 200 nm$$

Question 10

Which of the following best explains why oil immersion is used with high-power objective lenses?

Accepted Answer

Oil increases the refractive index, reducing light refraction and improving resolution

Question 11

A microbiologist wants to stain the background of a slide rather than the cells themselves. Which type of dye should be used?

Accepted Answer

Acidic dye

Question 12

Which step in the staining process is responsible for fixing the cells to the slide?

Accepted Answer

Fix

Question 13

A scientist is using a Transmission Electron Microscope (TEM) to study a specimen. What is the main advantage of TEM over light microscopy?

Accepted Answer

TEM provides greater magnification and resolution of internal structures

Question 14

Which of the following best describes the function of a mordant in the staining process?

Accepted Answer

It increases the affinity of the dye for the cell

Question 15

A microbiologist observes that the image under the microscope is blurry and lacks detail. Which adjustment should be made first?

Accepted Answer

Adjust the fine focus knob

Question 16

Which of the following is NOT a type of light microscope described in the study materials?

Accepted Answer

Scanning electron

Question 17

Why is it important to use a blue filter when trying to achieve higher resolution in light microscopy?

Accepted Answer

Blue light has a shorter wavelength, decreasing the limit of resolution

Question 18

Which staining technique would be most appropriate for visualizing bacterial capsules?

Accepted Answer

Capsule stain

Question 19

A cell is stained with a dye that has a positively charged chromophore. What type of dye is this?

Accepted Answer

Basic dye

Question 20

Which of the following best explains the principle of refraction in microscopy?

Accepted Answer

Refraction is the bending of light as it passes from one medium to another

Microscopy and Staining Techniques in Microbiology ~ Chp 3

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