SEMMELWEIS UNIVERSITY,
MEDICAL BIOPHYSICS - FINAL
EXAM 2026 QUESTIONS AND
ANSWERS
Coulter principle. - Answer -The ability to count and measure the size of particles
using an electric circuit. Particles are moved through a small aperture, their
presence causes a narrowing of the aperture, which leads to an increase in
resistance.By using constant I, According to Ohms law (U= I * R), when R
increases, U increases and pulse is generated.
Parts and functions of the Coulter-counter - Answer -- Two spaces with a small
aperture in between, capillary (contains the electrolyte solution with the cells)
- Measuring electrode, one in each of the spaces (closing the circuit and measuring
voltage between the two spaces)
- Pump (draws the solution into the smaller space, and out
again, through the capillary)
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,- Auxiliary electrode (signals when certain volume is
reached, to initiate pumping out of the solution)
- Integral Discriminator (filter out noise)
- Differential Discriminator (mapped of the size distribution
of the particles)
How does the voltage pulse amplitude depend on particle size in the Coulter-
counter? - Answer -Its proportional, bigger particle will form higher resistance,
higher voltage pulse.
How do you separate the red-blood-cell versus white-blood-cell signals in a
Coulter-counter? - Answer -when you want to measure RBC, it's not necessary to
separate them from the RBC b.c. the number of WBC is negligible (less than error
of the measurement)
By hemolyze RBC and measured them separately photochemically and subtracted
the result from the coulter-counting measurement
How do you separate the red-blood-cell versus platelet signals in a Coulter-
counter? - Answer -By integral discrimination (the size of the platelets is much
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,smaller)
What is the role of differential discriminator in Coulter-counting? - Answer -
Mapping the size distribution of the particle
Why is dilution of blood is necessary in Coulter-counting? - Answer -Because the
cells themselves do not conduct well, and so we dilute them with an electrolyte
solution so changes in resistivity are noticed. Also, for practical reasons (e.g. we
don't want the solution to dry up.)
What solution is used for blood dilution in Coulter-counting? - Answer -Saline
solution, for optimal osmotic pressure (keep the RBCs in their natural size) and for
good conduction (NaCl)
How does the matter flow density (flux) change if the concentration gradient is
doubled? - Answer -It doubles, due to flicks first law: Jv=-Dxdeltac/deltax
Name the parameters influencing the value of diffusion coefficient. - Answer -Size
and shape of the particle as well as the temperature and viscosity of the medium.
Can be calculated for spherical particles: D=kT/6 pi n r
What diffuses faster: a potassium ion or a virus particle? - Answer -K+ ion due to
smaller diffusion coefficient (smaller size)
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, How does the average distance travelled by a diffusing particle depend on time? -
Answer -Square root function (Distance average ^2 =6 * D * t)
On what length scale is diffusion an effective transport process? - Answer -On a
small scale
How does the minimum wavelength of the x-ray spectrum change with increasing
anode voltage? - Answer -Decreases (higher voltage higher kinetic energy higher
frequency spectrum) - Duane-hunt law
How does the minimum wavelength of the x-ray spectrum change with increasing
anode current? - Answer -Does not change
What is the maximum x-ray photon energy at 50 kV anode voltage? - Answer -50
keV
What elements are suitable as x-ray-tube anode material? - Answer -High melting
point and high atomic number materials molybdenum
(more common in medical diagnosis) and tungsten.
What are the x-ray spectral lines characteristic of? - Answer -Anode material
Why do we need to cool the x-ray-tube anode? - Answer -Because it heats up due
to low efficiency in the conversion of high
kinetic energy to x-ray.
©COPYRIGHT 2025, ALL RIGHTS RESERVED 4
MEDICAL BIOPHYSICS - FINAL
EXAM 2026 QUESTIONS AND
ANSWERS
Coulter principle. - Answer -The ability to count and measure the size of particles
using an electric circuit. Particles are moved through a small aperture, their
presence causes a narrowing of the aperture, which leads to an increase in
resistance.By using constant I, According to Ohms law (U= I * R), when R
increases, U increases and pulse is generated.
Parts and functions of the Coulter-counter - Answer -- Two spaces with a small
aperture in between, capillary (contains the electrolyte solution with the cells)
- Measuring electrode, one in each of the spaces (closing the circuit and measuring
voltage between the two spaces)
- Pump (draws the solution into the smaller space, and out
again, through the capillary)
©COPYRIGHT 2025, ALL RIGHTS RESERVED 1
,- Auxiliary electrode (signals when certain volume is
reached, to initiate pumping out of the solution)
- Integral Discriminator (filter out noise)
- Differential Discriminator (mapped of the size distribution
of the particles)
How does the voltage pulse amplitude depend on particle size in the Coulter-
counter? - Answer -Its proportional, bigger particle will form higher resistance,
higher voltage pulse.
How do you separate the red-blood-cell versus white-blood-cell signals in a
Coulter-counter? - Answer -when you want to measure RBC, it's not necessary to
separate them from the RBC b.c. the number of WBC is negligible (less than error
of the measurement)
By hemolyze RBC and measured them separately photochemically and subtracted
the result from the coulter-counting measurement
How do you separate the red-blood-cell versus platelet signals in a Coulter-
counter? - Answer -By integral discrimination (the size of the platelets is much
©COPYRIGHT 2025, ALL RIGHTS RESERVED 2
,smaller)
What is the role of differential discriminator in Coulter-counting? - Answer -
Mapping the size distribution of the particle
Why is dilution of blood is necessary in Coulter-counting? - Answer -Because the
cells themselves do not conduct well, and so we dilute them with an electrolyte
solution so changes in resistivity are noticed. Also, for practical reasons (e.g. we
don't want the solution to dry up.)
What solution is used for blood dilution in Coulter-counting? - Answer -Saline
solution, for optimal osmotic pressure (keep the RBCs in their natural size) and for
good conduction (NaCl)
How does the matter flow density (flux) change if the concentration gradient is
doubled? - Answer -It doubles, due to flicks first law: Jv=-Dxdeltac/deltax
Name the parameters influencing the value of diffusion coefficient. - Answer -Size
and shape of the particle as well as the temperature and viscosity of the medium.
Can be calculated for spherical particles: D=kT/6 pi n r
What diffuses faster: a potassium ion or a virus particle? - Answer -K+ ion due to
smaller diffusion coefficient (smaller size)
©COPYRIGHT 2025, ALL RIGHTS RESERVED 3
, How does the average distance travelled by a diffusing particle depend on time? -
Answer -Square root function (Distance average ^2 =6 * D * t)
On what length scale is diffusion an effective transport process? - Answer -On a
small scale
How does the minimum wavelength of the x-ray spectrum change with increasing
anode voltage? - Answer -Decreases (higher voltage higher kinetic energy higher
frequency spectrum) - Duane-hunt law
How does the minimum wavelength of the x-ray spectrum change with increasing
anode current? - Answer -Does not change
What is the maximum x-ray photon energy at 50 kV anode voltage? - Answer -50
keV
What elements are suitable as x-ray-tube anode material? - Answer -High melting
point and high atomic number materials molybdenum
(more common in medical diagnosis) and tungsten.
What are the x-ray spectral lines characteristic of? - Answer -Anode material
Why do we need to cool the x-ray-tube anode? - Answer -Because it heats up due
to low efficiency in the conversion of high
kinetic energy to x-ray.
©COPYRIGHT 2025, ALL RIGHTS RESERVED 4
