Microscope Practice Questions
20 free Microscope practice questions for the General Science. Tap an option to answer — you get instant feedback, the correct answer, and a detailed explanation for every question.
Which part of a compound microscope is responsible for regulating the amount of light that reaches the specimen?
- A Objective lens
- B Eyepiece
- C Iris diaphragm
- D Coarse adjustment knob
Correct answer: Iris diaphragm
The iris diaphragm is located under the stage and can be opened or closed to control the intensity and size of the cone of light. Proper adjustment of the diaphragm helps in improving the contrast and resolution of the image.
If a microscope has an eyepiece with 10x magnification and an objective lens with 40x magnification, what is the total magnification of the specimen?
- A 50x
- B 400x
- C 40x
- D 100x
Correct answer: 400x
The total magnification is calculated by multiplying the magnification of the ocular lens (eyepiece) by the magnification of the objective lens. In this case, 10 multiplied by 40 equals 400x.
Which type of microscope is specifically designed to provide a three-dimensional view of a specimen at relatively low magnification?
- A Compound light microscope
- B Transmission electron microscope
- C Stereo (dissecting) microscope
- D Phase-contrast microscope
Correct answer: Stereo (dissecting) microscope
Stereo microscopes utilize two separate optical paths with two eyepieces and two objectives to provide slightly different viewing angles to each eye. This creates a 3D effect suitable for dissecting or examining large, opaque objects.
In an electron microscope, what is used instead of glass lenses to focus the beam of electrons?
- A Mirrors
- B Electromagnetic lenses
- C Prisms
- D Fiber optics
Correct answer: Electromagnetic lenses
Electromagnetic lenses are coils of wire that create magnetic fields to bend and focus the electron beam. Since electrons are charged particles, their path can be precisely manipulated by these magnetic fields.
Which objective lens should always be in place when you first begin to focus a specimen on a compound microscope?
- A Low power (4x or 10x)
- B High power (40x)
- C Oil immersion (100x)
- D It does not matter
Correct answer: Low power (4x or 10x)
Starting with the lowest power objective provides the widest field of view, making it easier to locate the specimen. It also minimizes the risk of the lens hitting the slide during coarse focusing.
What is the primary function of the condenser lens in a microscope?
- A To magnify the image further
- B To focus light onto the specimen
- C To change the color of the light
- D To hold the slide in place
Correct answer: To focus light onto the specimen
The condenser sits below the stage and gathers light from the illuminator, concentrating it into a sharp cone that illuminates the specimen. This is crucial for achieving high resolution at higher magnifications.
Which scientist is often called the 'Father of Microscopy' for his improvements to the microscope and discovery of microorganisms?
- A Robert Hooke
- B Antonie van Leeuwenhoek
- C Louis Pasteur
- D Matthias Schleiden
Correct answer: Antonie van Leeuwenhoek
Leeuwenhoek crafted high-quality single-lens microscopes that were capable of magnifications up to 270x. He was the first to observe and describe bacteria, sperm cells, and yeast, which he called 'animalcules'.
What is the term for the ability of a microscope to distinguish two close points as separate entities?
- A Magnification
- B Refraction
- C Resolution
- D Contrast
Correct answer: Resolution
Resolution (or resolving power) is the limit of usable magnification; without it, an image just becomes a larger blur. It is determined primarily by the wavelength of light and the numerical aperture of the lenses.
Why is immersion oil used with a 100x objective lens?
- A To lubricate the lens and prevent scratching
- B To keep the specimen from drying out
- C To prevent the refraction of light and increase numerical aperture
- D To make the specimen appear larger
Correct answer: To prevent the refraction of light and increase numerical aperture
Immersion oil has the same refractive index as glass, which prevents light from bending as it leaves the slide and enters the air. This allows more light to be captured by the lens, significantly improving the resolution.
In a microscope, the 'Field of View' refers to which of the following?
- A The total height of the microscope
- B The area of the specimen that is visible through the lenses
- C The distance between the objective lens and the stage
- D The brightness of the light source
Correct answer: The area of the specimen that is visible through the lenses
The field of view is the circular area seen when looking through the eyepiece. As magnification increases, the diameter of the field of view decreases, meaning you see less of the overall specimen but in greater detail.
Which part of the microscope should ONLY be used with the low-power objective lens?
- A Fine adjustment knob
- B Iris diaphragm
- C Coarse adjustment knob
- D Mechanical stage
Correct answer: Coarse adjustment knob
The coarse adjustment knob moves the stage rapidly. Using it with high-power objectives can cause the lens to crash into the slide, potentially damaging both the expensive lens and the specimen.
Which type of microscopy is best suited for viewing the internal structures of extremely thin sections of cells at high magnification?
- A Scanning Electron Microscopy (SEM)
- B Transmission Electron Microscopy (TEM)
- C Fluorescence Microscopy
- D Dark-field Microscopy
Correct answer: Transmission Electron Microscopy (TEM)
TEM passes a beam of electrons through an ultra-thin specimen. The resulting image provides incredible detail of internal organelles and structures at the molecular level.
The term 'Parfocal' in microscopy means that:
- A The microscope uses two eyepieces
- B The focus is preserved when switching objectives
- C The microscope can be used without a light source
- D The magnification is infinite
Correct answer: The focus is preserved when switching objectives
A parfocal microscope is designed so that the distance from the objective to the specimen remains nearly constant. This allows the user to switch objectives with only minimal refocusing using the fine adjustment knob.
Which type of microscope uses ultraviolet light to excite specimens that have been treated with specific dyes?
- A Phase-contrast microscope
- B Fluorescence microscope
- C Polarizing microscope
- D Inverted microscope
Correct answer: Fluorescence microscope
Fluorescence microscopes use high-intensity light to excite fluorescent molecules (fluorophores) in the specimen. These molecules then emit light of a longer wavelength, allowing specific components of a cell to be visualized.
The 'Working Distance' of a microscope is defined as the distance between:
- A The eyepiece lens and the objective lens
- B The objective and the specimen
- C The stage and the base
- D The user's eye and the eyepiece
Correct answer: The objective and the specimen
Working distance is the physical space between the front element of the objective lens and the specimen. As the magnification and numerical aperture of the lens increase, the working distance generally decreases.
Scanning Electron Microscopy (SEM) is primarily used to visualize which of the following?
- A Living bacteria in water
- B Specimen surface and 3D structure
- C The individual atoms of a crystal
- D The DNA sequence inside a nucleus
Correct answer: Specimen surface and 3D structure
SEM scans a focused beam of electrons across the surface of a specimen coated in metal. The reflected (secondary) electrons are detected to create a detailed, 3D-like image of the specimen's exterior.
Which component of the microscope is a platform that supports the slide being viewed?
- A Base
- B Arm
- C Stage
- D Revolving nosepiece
Correct answer: Stage
The stage is the flat plate where the slide is placed. Most modern microscopes have a mechanical stage that allows for precise movement of the slide in the X and Y directions.
In microscopy, 'Contrast' refers to the ability to:
- A Make an object look larger
- B Distinguish specimen from its background
- C Focus the light onto a point
- D Switch between different objective lenses
Correct answer: Distinguish specimen from its background
Contrast is the difference in light intensity or color between the specimen and the surrounding medium. It is often enhanced by staining the specimen or by using specialized optics like phase-contrast.
An 'Inverted Microscope' is different from a standard compound microscope because:
- A Objectives below, condenser and light above
- B It uses no lenses, only mirrors
- C It can only be used in total darkness
- D The viewed image appears upside down and reversed
Correct answer: Objectives below, condenser and light above
Inverted microscopes are useful for observing living cells at the bottom of a large container (like a tissue culture flask). Having the objectives underneath allows the lens to get close to the cells despite the volume of liquid above them.
What happens to the brightness of the image as you move from low power to high power magnification?
- A The brightness increases
- B The brightness decreases
- C The brightness stays the same
- D The light turns a different color
Correct answer: The brightness decreases
High-power objective lenses have smaller apertures, which allow less light to enter. Therefore, when you increase magnification, you typically need to increase the light intensity using the diaphragm or the illuminator control.