SEMMELWEIS UNIVERSITY, MEDICAL BIOPHYSICS - FINAL EXAM
ACTUAL QUESTIONS AND CORRECT ANSWERS| UPDATED
Coulter principle.
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
- 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)
- 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?
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?
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?
By integral discrimination (the size of the platelets is much
smaller)
What is the role of differential discriminator in Coulter-counting?
Mapping the size distribution of the particle
Why is dilution of blood is necessary in Coulter-counting?
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?
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?
It doubles, due to flicks first law: Jv=-Dxdeltac/deltax
Name the parameters influencing the value of diffusion coefficient.
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?
K+ ion due to smaller diffusion coefficient (smaller size)
How does the average distance travelled by a diffusing particle depend on time?
Square root function (Distance average ^2 =6 D t)
On what length scale is diffusion an effective transport process?
On a small scale
How does the minimum wavelength of the x-ray spectrum change with increasing anode
voltage?
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?
Does not change
What is the maximum x-ray photon energy at 50 kV anode voltage?
50 keV
What elements are suitable as x-ray-tube anode material?
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?
Anode material
Why do we need to cool the x-ray-tube anode?
Because it heats up due to low efficiency in the conversion of high
kinetic energy to x-ray.
How does x-ray absorbance depend on the atomic number of
ACTUAL QUESTIONS AND CORRECT ANSWERS| UPDATED
Coulter principle.
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
- 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)
- 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?
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?
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?
By integral discrimination (the size of the platelets is much
smaller)
What is the role of differential discriminator in Coulter-counting?
Mapping the size distribution of the particle
Why is dilution of blood is necessary in Coulter-counting?
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?
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?
It doubles, due to flicks first law: Jv=-Dxdeltac/deltax
Name the parameters influencing the value of diffusion coefficient.
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?
K+ ion due to smaller diffusion coefficient (smaller size)
How does the average distance travelled by a diffusing particle depend on time?
Square root function (Distance average ^2 =6 D t)
On what length scale is diffusion an effective transport process?
On a small scale
How does the minimum wavelength of the x-ray spectrum change with increasing anode
voltage?
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?
Does not change
What is the maximum x-ray photon energy at 50 kV anode voltage?
50 keV
What elements are suitable as x-ray-tube anode material?
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?
Anode material
Why do we need to cool the x-ray-tube anode?
Because it heats up due to low efficiency in the conversion of high
kinetic energy to x-ray.
How does x-ray absorbance depend on the atomic number of
