What does setting up Köhler illumination on a bright-field microscope mainly give?

An evenly lit field with the best resolution and contrast

A dark background against which unstained cells shine

A higher total magnification with the same lenses

Fluorescent light from the specimen itself

Blood is drawn from a driver for a medico-legal blood alcohol estimation. What should the venepuncture site be cleaned with?

Aqueous povidone-iodine or soap and water

Rectified spirit on a cotton swab

Ether, allowed to evaporate fully

After examining oil-immersion slides, a technician turns to the 40x dry objective. At 40x the image is milky and will not sharpen, while the 10x and 100x images of the same slide are clear. The most likely cause is:

Immersion oil smeared on the 40x front lens

Slide placed on the stage upside down

Lamp voltage set too low for 40x

Condenser iris diaphragm closed too far

Basic medical laboratory, ethics and microscopes

18 Kerala MSc MLT Entrance practice questions on Basic medical laboratory, ethics and microscopes, part of Pathology. The first 18 are below; the first 5 with answers and explanations (tap Show answer after you have chosen), the rest in Learn with a free account.

Question 1 · Medium
What does setting up Köhler illumination on a bright-field microscope mainly give?
1. AA dark background against which unstained cells shine
2. BA higher total magnification with the same lenses
3. CAn evenly lit field with the best resolution and contrast
4. DFluorescent light from the specimen itself
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Answer: C · An evenly lit field with the best resolution and contrast
In Köhler illumination the field diaphragm is focused in the specimen plane by the condenser, and the condenser is centred. The lamp filament is then out of focus in the specimen plane, so the field is evenly lit without glare. The aperture diaphragm is then opened to about 70-80% of the objective's numerical aperture, which gives the best balance of resolution and contrast. Magnification is not changed.
- A: A dark background is the purpose of dark-field illumination.
- B: Magnification depends only on the objective and eyepiece.
- D: Fluorescence needs an excitation source and filters.
Question 2 · Medium
Blood is drawn from a driver for a medico-legal blood alcohol estimation. What should the venepuncture site be cleaned with?
1. AAqueous povidone-iodine or soap and water
2. BRectified spirit on a cotton swab
3. CA 70% isopropyl alcohol swab
4. DEther, allowed to evaporate fully
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Answer: A · Aqueous povidone-iodine or soap and water
Any alcohol-based skin antiseptic can carry alcohol into the sample and falsely raise the result, which a defence lawyer can challenge. A non-alcoholic antiseptic such as aqueous povidone-iodine, chlorhexidine in water or soap and water is used. The sample is collected in a fluoride tube, sealed, labelled and handed over with a signed chain of custody. These steps make the result legally defensible.
- B: Rectified spirit is ethanol, the very substance being measured.
- C: Isopropyl alcohol can contaminate the sample and interfere with the result.
- D: Ether is volatile and flammable and is not a recommended skin preparation for this test.
Question 3 · Easy
Explaining the purpose, benefits and risks of an HIV test to a patient and getting the patient's agreement before the sample is taken is called what?
1. AConfidentiality
2. BBeneficence
3. CPre-test screening
4. DInformed consent
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Answer: D · Informed consent
Informed consent means the patient is told what the test is for, its benefits and risks and the alternatives, and agrees freely before it is done. Indian HIV testing policy (NACO) requires consent, counselling and confidentiality for every HIV test. Consent is recorded, and for minors it is given by a guardian. Testing without it is an ethical and legal breach.
- A: Confidentiality is keeping the result private, not obtaining agreement.
- B: Beneficence is the duty to act for the patient's good.
- C: Screening is a type of testing, not the process of agreement.
Question 4 · Hard
Useful magnification is about 500-1,000 times the numerical aperture. With a 40x objective of NA 0.65, which eyepiece gives the highest magnification without empty magnification?
1. A25x
2. B20x
3. C15x
4. D10x
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Answer: C · 15x
The upper limit is 1,000 x 0.65 = 650x. With a 15x eyepiece, the total is 40 x 15 = 600x, which is within the limit. A 20x eyepiece gives 800x and a 25x gives 1,000x: the image grows but no finer detail is resolved (empty magnification). A 10x eyepiece gives 400x, which is useful but not the highest possible.
- A: A 25x eyepiece gives 1,000x, well into empty magnification.
- B: A 20x eyepiece gives 800x, above the 650x limit.
- D: A 10x eyepiece gives 400x, below the highest useful value.
Question 5 · Hard
After examining oil-immersion slides, a technician turns to the 40x dry objective. At 40x the image is milky and will not sharpen, while the 10x and 100x images of the same slide are clear. The most likely cause is:
1. ASlide placed on the stage upside down
2. BLamp voltage set too low for 40x
3. CImmersion oil smeared on the 40x front lens
4. DCondenser iris diaphragm closed too far
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Answer: C · Immersion oil smeared on the 40x front lens
The problem is confined to one objective, so it lies in that objective. The 40x lens has a short working distance and often dips into oil when the nosepiece is swung through an oiled slide. A film of oil on its front lens gives a milky, unsharp image. Cleaning it with lens tissue and lens cleaner restores the image.
- A: An upside-down slide also stops the 100x objective from focusing.
- B: A dim lamp would affect all objectives and darken rather than blur the image.
- D: A closed iris would affect every objective and gives a dark, contrasty image rather than milkiness.
Question 6 · Medium
A patient's brother phones the laboratory and asks for the patient's HIV test result. What should the technologist do?
1. AGive it only after confirming his identity and relationship
2. BGive it after confirming the patient's age
3. CDecline, and release it only to the patient or the doctor
4. DGive it only if the result is negative
Answer and explanation in LearnFree account
Question 7 · Medium
In a humid coastal laboratory, how should microscopes be stored to prevent fungal growth on the lenses?
1. AIn the laboratory cold room
2. BIn a dry cabinet with silica gel or a warm bulb
3. CSealed airtight in a plastic bag
4. DWith the eyepieces removed to air the tubes
Answer and explanation in LearnFree account
Question 8 · Easy
Objectives that stay nearly in focus when the nosepiece is turned from one to the next are described as:
1. AAchromatic
2. BParfocal
3. CApochromatic
4. DParcentric
Answer and explanation in LearnFree account
Question 9 · Easy
When focusing with the 100x oil-immersion objective, only the fine adjustment is used because:
1. AThe condenser must stay fixed
2. BThe coarse knob does not move the stage
3. CIts working distance is very short
4. DOil blocks the coarse adjustment
Answer and explanation in LearnFree account
Question 10 · Hard
A technician pricks a finger with a needle just used to draw blood from a patient known to be HIV-positive. Which plan follows NACO guidance?
1. AStart PEP only after the technician's own baseline HIV result is back
2. BSqueeze the wound to bleed it, apply bleach and start PEP after 72 hours
3. CWait for the patient's repeat HIV test before washing the site
4. DWash with soap and water without squeezing; start PEP as early as possible
Answer and explanation in LearnFree account
Question 11 · Medium
Studies of laboratory errors consistently show that most of them arise in which phase of testing?
1. APre-analytical phase
2. BPost-analytical phase
3. CAnalytical phase
4. DInstrument calibration phase
Answer and explanation in LearnFree account
Question 12 · Medium
Hyaline casts and unstained living cells are easier to see with a phase-contrast microscope because it:
1. ALights the specimen only from the side on a dark field
2. BIncreases magnification beyond that of bright-field lenses
3. CConverts phase differences in light into differences in brightness
4. DUses ultraviolet light that makes the specimen glow
Answer and explanation in LearnFree account
Question 13 · Medium
A centrifuge motor catches fire in the laboratory. After switching off the power at the mains, which extinguisher is the safest to use?
1. ACarbon dioxide
2. BWater
3. CSoda-acid
4. DMechanical foam
Answer and explanation in LearnFree account
Question 14 · Hard
A technician sees a dark speck in the field at every magnification. It does not move when the slide is moved, and it turns round when the eyepiece is rotated in its tube. Where is the dirt?
1. AOn the condenser top lens
2. BOn the eyepiece lens
3. COn the slide or coverslip
4. DOn the front lens of the objective
Answer and explanation in LearnFree account
Question 15 · Easy
The limit of resolution of a good bright-field light microscope using oil immersion is about:
1. A0.02 µm
2. B0.2 µm
3. C20 µm
4. D2 µm
Answer and explanation in LearnFree account
Question 16 · Medium
A conscious adult patient, told the purpose and risks of a blood test, refuses it. The laboratory respects the refusal. This follows the ethical principle of:
1. ABeneficence
2. BJustice
3. CAutonomy
4. DNon-maleficence
Answer and explanation in LearnFree account
Question 17 · Medium
For a medico-legal specimen, the documented record of every person who collected, handled, stored and tested it is called the:
1. AInformed consent record
2. BInternal quality control log
3. CChain of custody
4. DRequisition form
Answer and explanation in LearnFree account
Question 18 · Hard
A stained blood film is in sharp focus under the 10x objective, but with the 100x oil objective no image can be found even when the lens touches the oil. The oil and objective are clean. What is the most likely cause?
1. AToo much immersion oil has been applied
2. BThe slide has been placed upside down on the stage
3. CThe 100x objective is not parfocal with the others
4. DThe condenser iris diaphragm is fully open
Answer and explanation in LearnFree account

Basic medical laboratory, ethics and microscopes

What does setting up Köhler illumination on a bright-field microscope mainly give?

Blood is drawn from a driver for a medico-legal blood alcohol estimation. What should the venepuncture site be cleaned with?

Explaining the purpose, benefits and risks of an HIV test to a patient and getting the patient's agreement before the sample is taken is called what?

Useful magnification is about 500-1,000 times the numerical aperture. With a 40x objective of NA 0.65, which eyepiece gives the highest magnification without empty magnification?

After examining oil-immersion slides, a technician turns to the 40x dry objective. At 40x the image is milky and will not sharpen, while the 10x and 100x images of the same slide are clear. The most likely cause is:

A patient's brother phones the laboratory and asks for the patient's HIV test result. What should the technologist do?

In a humid coastal laboratory, how should microscopes be stored to prevent fungal growth on the lenses?

Objectives that stay nearly in focus when the nosepiece is turned from one to the next are described as:

When focusing with the 100x oil-immersion objective, only the fine adjustment is used because:

A technician pricks a finger with a needle just used to draw blood from a patient known to be HIV-positive. Which plan follows NACO guidance?

Studies of laboratory errors consistently show that most of them arise in which phase of testing?

Hyaline casts and unstained living cells are easier to see with a phase-contrast microscope because it:

A centrifuge motor catches fire in the laboratory. After switching off the power at the mains, which extinguisher is the safest to use?

A technician sees a dark speck in the field at every magnification. It does not move when the slide is moved, and it turns round when the eyepiece is rotated in its tube. Where is the dirt?

The limit of resolution of a good bright-field light microscope using oil immersion is about:

A conscious adult patient, told the purpose and risks of a blood test, refuses it. The laboratory respects the refusal. This follows the ethical principle of:

For a medico-legal specimen, the documented record of every person who collected, handled, stored and tested it is called the:

A stained blood film is in sharp focus under the 10x objective, but with the 100x oil objective no image can be found even when the lens touches the oil. The oil and objective are clean. What is the most likely cause?