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SEMMELWEIS UNIVERSITY MEDICAL BIOPHYSICS —
FINAL EXAM 2026/2027 Academic Year.
Question 1 (Multiple Choice)
A Coulter counter measures blood cells by drawing a diluted sample through a small aperture.
According to Ohm's Law, what happens to the voltage measured across the aperture when a
non-conductive blood cell passes through?
A) Voltage decreases because resistance decreases
B) Voltage increases because resistance increases [CORRECT]
C) Voltage remains constant because current changes proportionally
D) Voltage decreases because capacitance increases
Rationale: According to Ohm's Law (U = I × R), when a constant current is maintained and a
non-conductive particle enters the aperture, the resistance (R) increases due to the
displacement of conductive electrolyte. Since current (I) is held constant, the voltage (U)
across the aperture increases proportionally. This voltage pulse is the fundamental signal
detected by the Coulter counter. Clinically, this principle enables rapid and accurate
enumeration of thousands of cells per second, forming the basis of automated complete
blood count (CBC) analysis.
Question 2 (True/False)
In a Coulter counter, the voltage pulse amplitude is inversely proportional to the particle size
passing through the aperture.
A) True
B) False [CORRECT]
Rationale: The voltage pulse amplitude is directly proportional to the particle size, not
inversely proportional. A larger particle displaces more electrolyte, causing a greater increase
in resistance and thus a higher voltage pulse. This direct proportionality is essential for the
Coulter counter to simultaneously count and size particles, allowing differentiation between
cell populations such as red blood cells, white blood cells, and platelets in clinical hematology.
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Question 3 (Multiple Choice)
Which component of the Coulter counter is responsible for ensuring that only particles within
a specific size range are counted and mapped?
A) Auxiliary electrode
B) Integral discriminator
C) Differential discriminator [CORRECT]
D) Peristaltic pump
Rationale: The differential discriminator maps the size distribution of particles by analyzing
voltage pulse amplitudes. It discriminates between pulses of different heights, allowing the
construction of a histogram that represents the size distribution of the cell population. This is
clinically critical for identifying abnormal cell distributions, such as microcytic or macrocytic
red blood cells in anemia, or elevated platelet counts in thrombocytosis.
Question 4 (Multiple Choice)
What is the primary function of the integral discriminator in a Coulter counter?
A) To map the size distribution of particles
B) To filter out noise and pulses below a threshold voltage [CORRECT]
C) To generate the constant current through the aperture
D) To hemolyze red blood cells before counting
Rationale: The integral discriminator filters out low-amplitude noise and unwanted small
pulses by establishing a voltage threshold. Only pulses exceeding this threshold are counted,
ensuring that electronic noise and debris do not contaminate the cell count. This improves the
accuracy and reliability of clinical blood counts, preventing false elevations in cell counts that
could lead to misdiagnosis.
Question 5 (Select All That Apply)
Which of the following are essential components of a Coulter counter system? (Select all that
apply)
A) Capillary aperture [CORRECT]
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B) Measuring electrodes in each chamber [CORRECT]
C) Differential discriminator [CORRECT]
D) Hemolysis reagent for WBC counting [CORRECT]
E) Gas chromatography column
Rationale: The Coulter counter requires: (1) a capillary aperture through which cells pass; (2)
measuring electrodes in each chamber to detect resistance changes; (3) a differential
discriminator to map size distributions; and (4) a hemolysis reagent when performing white
blood cell counting to lyse RBCs so WBCs can be measured. Gas chromatography is unrelated
to Coulter counting. Understanding these components is essential for troubleshooting
instrument errors in clinical laboratories and ensuring accurate CBC results.
Question 6 (Multiple Choice)
A clinical laboratory technician observes that platelets produce small voltage pulses while red
blood cells produce larger pulses in a Coulter counter. What physical principle explains this
observation?
A) The Nernst equation
B) The direct proportionality between pulse amplitude and particle volume [CORRECT]
C) The inverse square law of electrical fields
D) The Doppler effect on electrical conductivity
Rationale: The voltage pulse amplitude is directly proportional to the particle volume (size).
Platelets are much smaller than red blood cells (approximately 2–3 μm vs. 6–8 μm), so they
displace less electrolyte and produce smaller resistance changes, resulting in lower voltage
pulses. This size-dependent response allows the Coulter counter to differentiate and count
distinct cell populations, which is fundamental to automated platelet and red blood cell
enumeration in clinical diagnostics.
Question 7 (Multiple Choice)
When performing a complete blood count using a Coulter counter, why is it generally
unnecessary to physically separate white blood cells from red blood cells before counting red
blood cells?
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A) WBCs are hemolyzed by the saline diluent
B) The number of WBCs is negligible compared to RBCs and falls within the measurement
error [CORRECT]
C) WBCs and RBCs have identical electrical properties
D) The integral discriminator automatically removes all WBC signals
Rationale: In normal human blood, the red blood cell count is approximately 4.5–5.5 million
per μL, while the white blood cell count is only 4,000–11,000 per μL—a ratio of roughly 500:1.
The WBC contribution to the total count is less than 0.2%, which is within the instrument's
measurement error. Therefore, for routine RBC counting, WBC interference is clinically
insignificant, and no separation is required. This simplifies the CBC workflow and reduces
processing time in clinical laboratories.
Question 8 (Select All That Apply)
Which methods can be used to obtain an accurate white blood cell count when using a
Coulter counter? (Select all that apply)
A) Hemolyzing red blood cells and counting the remaining white blood cells [CORRECT]
B) Measuring total cells (RBC + WBC) and subtracting the WBC count obtained by
photochemical measurement [CORRECT]
C) Physical filtration through a 5 μm membrane to remove all RBCs
D) Using the differential discriminator to exclude all pulses below a specific threshold
E) Centrifuging the sample and counting only the buffy coat layer
Rationale: Accurate WBC counting requires eliminating the overwhelming numerical
dominance of RBCs. Methods include: (1) hemolyzing RBCs with a lysing agent so only WBC
nuclei remain for counting; and (2) measuring total cells via Coulter counting and subtracting
the RBC count obtained through an alternative method such as photochemical measurement.
Physical filtration and buffy coat counting are not standard Coulter counter procedures. These
methods ensure accurate WBC enumeration, which is critical for diagnosing infections,
leukemia, and immunodeficiency disorders.
Question 9 (Multiple Choice)
SEMMELWEIS UNIVERSITY MEDICAL BIOPHYSICS —
FINAL EXAM 2026/2027 Academic Year.
Question 1 (Multiple Choice)
A Coulter counter measures blood cells by drawing a diluted sample through a small aperture.
According to Ohm's Law, what happens to the voltage measured across the aperture when a
non-conductive blood cell passes through?
A) Voltage decreases because resistance decreases
B) Voltage increases because resistance increases [CORRECT]
C) Voltage remains constant because current changes proportionally
D) Voltage decreases because capacitance increases
Rationale: According to Ohm's Law (U = I × R), when a constant current is maintained and a
non-conductive particle enters the aperture, the resistance (R) increases due to the
displacement of conductive electrolyte. Since current (I) is held constant, the voltage (U)
across the aperture increases proportionally. This voltage pulse is the fundamental signal
detected by the Coulter counter. Clinically, this principle enables rapid and accurate
enumeration of thousands of cells per second, forming the basis of automated complete
blood count (CBC) analysis.
Question 2 (True/False)
In a Coulter counter, the voltage pulse amplitude is inversely proportional to the particle size
passing through the aperture.
A) True
B) False [CORRECT]
Rationale: The voltage pulse amplitude is directly proportional to the particle size, not
inversely proportional. A larger particle displaces more electrolyte, causing a greater increase
in resistance and thus a higher voltage pulse. This direct proportionality is essential for the
Coulter counter to simultaneously count and size particles, allowing differentiation between
cell populations such as red blood cells, white blood cells, and platelets in clinical hematology.
, 2
Question 3 (Multiple Choice)
Which component of the Coulter counter is responsible for ensuring that only particles within
a specific size range are counted and mapped?
A) Auxiliary electrode
B) Integral discriminator
C) Differential discriminator [CORRECT]
D) Peristaltic pump
Rationale: The differential discriminator maps the size distribution of particles by analyzing
voltage pulse amplitudes. It discriminates between pulses of different heights, allowing the
construction of a histogram that represents the size distribution of the cell population. This is
clinically critical for identifying abnormal cell distributions, such as microcytic or macrocytic
red blood cells in anemia, or elevated platelet counts in thrombocytosis.
Question 4 (Multiple Choice)
What is the primary function of the integral discriminator in a Coulter counter?
A) To map the size distribution of particles
B) To filter out noise and pulses below a threshold voltage [CORRECT]
C) To generate the constant current through the aperture
D) To hemolyze red blood cells before counting
Rationale: The integral discriminator filters out low-amplitude noise and unwanted small
pulses by establishing a voltage threshold. Only pulses exceeding this threshold are counted,
ensuring that electronic noise and debris do not contaminate the cell count. This improves the
accuracy and reliability of clinical blood counts, preventing false elevations in cell counts that
could lead to misdiagnosis.
Question 5 (Select All That Apply)
Which of the following are essential components of a Coulter counter system? (Select all that
apply)
A) Capillary aperture [CORRECT]
, 3
B) Measuring electrodes in each chamber [CORRECT]
C) Differential discriminator [CORRECT]
D) Hemolysis reagent for WBC counting [CORRECT]
E) Gas chromatography column
Rationale: The Coulter counter requires: (1) a capillary aperture through which cells pass; (2)
measuring electrodes in each chamber to detect resistance changes; (3) a differential
discriminator to map size distributions; and (4) a hemolysis reagent when performing white
blood cell counting to lyse RBCs so WBCs can be measured. Gas chromatography is unrelated
to Coulter counting. Understanding these components is essential for troubleshooting
instrument errors in clinical laboratories and ensuring accurate CBC results.
Question 6 (Multiple Choice)
A clinical laboratory technician observes that platelets produce small voltage pulses while red
blood cells produce larger pulses in a Coulter counter. What physical principle explains this
observation?
A) The Nernst equation
B) The direct proportionality between pulse amplitude and particle volume [CORRECT]
C) The inverse square law of electrical fields
D) The Doppler effect on electrical conductivity
Rationale: The voltage pulse amplitude is directly proportional to the particle volume (size).
Platelets are much smaller than red blood cells (approximately 2–3 μm vs. 6–8 μm), so they
displace less electrolyte and produce smaller resistance changes, resulting in lower voltage
pulses. This size-dependent response allows the Coulter counter to differentiate and count
distinct cell populations, which is fundamental to automated platelet and red blood cell
enumeration in clinical diagnostics.
Question 7 (Multiple Choice)
When performing a complete blood count using a Coulter counter, why is it generally
unnecessary to physically separate white blood cells from red blood cells before counting red
blood cells?
, 4
A) WBCs are hemolyzed by the saline diluent
B) The number of WBCs is negligible compared to RBCs and falls within the measurement
error [CORRECT]
C) WBCs and RBCs have identical electrical properties
D) The integral discriminator automatically removes all WBC signals
Rationale: In normal human blood, the red blood cell count is approximately 4.5–5.5 million
per μL, while the white blood cell count is only 4,000–11,000 per μL—a ratio of roughly 500:1.
The WBC contribution to the total count is less than 0.2%, which is within the instrument's
measurement error. Therefore, for routine RBC counting, WBC interference is clinically
insignificant, and no separation is required. This simplifies the CBC workflow and reduces
processing time in clinical laboratories.
Question 8 (Select All That Apply)
Which methods can be used to obtain an accurate white blood cell count when using a
Coulter counter? (Select all that apply)
A) Hemolyzing red blood cells and counting the remaining white blood cells [CORRECT]
B) Measuring total cells (RBC + WBC) and subtracting the WBC count obtained by
photochemical measurement [CORRECT]
C) Physical filtration through a 5 μm membrane to remove all RBCs
D) Using the differential discriminator to exclude all pulses below a specific threshold
E) Centrifuging the sample and counting only the buffy coat layer
Rationale: Accurate WBC counting requires eliminating the overwhelming numerical
dominance of RBCs. Methods include: (1) hemolyzing RBCs with a lysing agent so only WBC
nuclei remain for counting; and (2) measuring total cells via Coulter counting and subtracting
the RBC count obtained through an alternative method such as photochemical measurement.
Physical filtration and buffy coat counting are not standard Coulter counter procedures. These
methods ensure accurate WBC enumeration, which is critical for diagnosing infections,
leukemia, and immunodeficiency disorders.
Question 9 (Multiple Choice)
