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SEMMELWEIS UNIVERSITY Medical Biophysics I. Semifinal - Theory topics Exam Questions and Answers
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SEMMELWEIS UNIVERSITY Medical Biophysics I. Semifinal - Theory topics Exam
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SEMMELWEIS UNIVERSITY MedicalBiophysics I. Semifinal - Theory topics
Exam
Types of radiation - Correct Answers -according to energy transfer: Electromagnetic
(light), mechanical (sound), particle (alpha)
according to interaction with matter: ionizing (alpha), nonionizing (sound)
Dependance of irradiance on distance from the source - Correct Answers -Irradiance is
the incident radiation on a target. The dependence on distance from the source varies
with the type of source. Assuming there is no attenuation:
● Point like source: irradiance is inversely proportional to the squared distancefrom the
source.
● Cylindrical source: irradiance is inversely proportional to the distance from the source.
● Planar source: irradiance does not change with increasing distance from the source
(as long as the distance is increased perpendicular to the plane and is not greater than
the linear size of the source)
If the distance from the source is not perpendicular: Ei=Einc,maxCosalpha
Fundamentals of geometric optics - Correct Answers -When light propagates through
slits which are much larger than its wavelength, we can consider the wavefront as a
line. This simplification allows us to calculate optical imaging with relative ease.
Radiometric Quantities - Correct Answers -Characterising the source:
Radiant power (W=J/s) P = ΔE/Δt
Radiant emittance and irradiance (W/ m2 )
M=ΔP/ΔA
Einc=ΔP/ΔA inc
Characterising the radiation:
Radiant flux (W=J/s) IE= ΔE Δt
Intensity JE = ΔIE/ΔA
Attenuation law - Correct Answers -J=J0xe^-müx
Fermat's Principle - Correct Answers -Light will choose the path which takes the least
amount of time (i.e spend the least amount of time in the slower medium). Is the basis
for the phenomenon of refraction and reflection.
,Law of Refraction (Snell's Law) - Correct Answers -Incident and refracted ray together
with the normal line (=optical axis) are all located on the same plane.
Snell's law: (sin alpha/sin beta) = c1/c2 = n21
Law of reflection. - Correct Answers -Angle of incidence = angle of reflection
Incident beam, reflected beam and optical axis are in the same plane.
Total internal reflection and its applications. - Correct Answers -Occurs when light is
propagated from a higher refractive index thoward a medium with lower refr.index and
with a larger angle than the critical angle. The critical angle is calculated by this formula:
(1/sinBetac)= (n2/n1). Application: endoscopy
Image formation on a curved surface - Correct Answers -Lenses are curved surfaces on
which light rays refract.
If light rays meet, an image will form.
The angle of refraction depends on the index of refraction of the medium.
A diagram of this should begin with drawing a normal ray which passes through the
center of curvature, and travels perpendicular to the surface- no refraction!
The incident angle of other incoming rays needs to be measured with respect to the
normal.
Principal light rays - Correct Answers -In geometric optics, image formation is made by
emerging of 3 principal light rays (parallel,focal and center). In case of converging lens it
looks like this:
Lens combinations - Correct Answers -Lenses are combined in a compound
microscope to form a system of two lenses: objective and eye-piece lenses.
Image magnification can be manipulated by adjusting the distances between the lens
and specimen as well as the distance between the two lenses.
refractive power - Correct Answers -the degree to which lenses are able to converge or
diverge light.
formula: D=1/f (f=focal point)
lens equation - Correct Answers -Reciprocal of the image distance plus the reciprocal of
the object distance, gives the reciprocal of the focal point, which equals the refractive
power.
Image formation by the light microscope - Correct Answers -
Concepts of magnification and angular magnification. - Correct Answers -magnification
is the ratio b/w image and object sizeangular magnification define as the ration b/w tan
beta(angle of the image)e and tan alpha (the angle of the object)a.in case that the
image is form on the near point [M(angle)=(nearpoin /focal length)+1] (near
point=0.25meter) b. in case the image form at the infinity: M(angle)=nearpoint/focal
length
, Rules of image formation. - Correct Answers -Depending on where the object is placed
with respect to the focal point and double focal point, will determine the type of image
that will be formed.
● Object is beyond 2F: image is real, inverted and diminished.
● Object is at the double focal point: image is real, inverted and the same size.
● object is between 2F and F: image is real, inverted and magnified.
● Object is at F: image is (virtual, upright and magnified at infinity) - Magnifying glass
● Object is closer than F: image is virtual, upright and magnified.
Magnification in the light microscope. - Correct Answers -The product of the
magnifications of the objective lense and the eyepiece lense: M=I/Ox(I'/O')=MoxMe
Oscillations. - Correct Answers -Phenomenon in which quantity varies as a function of
time around an equilibrium value
Diffraction on an optical grating. - Correct Answers -A structure with periodic optical
properties. Its characteristic feature is the grating period (d) with a size on the order of
the wavelength.
Polarization of light. - Correct Answers -A process which unpolarised light (light whose
electric field vectors propagate in more than 1 plane, which contains the direction of
propagation) become polarized light (light whose electric field vectors propagate only in
1 plane, which contains the direction of propagation) by an optical filter (polarizer)
Types of waves. - Correct Answers -Sound waves (longitudinal or transverse) - require
a medium
Electromagnetic waves (transverse waves) - do not require a medium
Matter wave (matter can act as a wave; electrons can have wavelike interference)
Limit of resolution of the light microscope. - Correct Answers -The smallest noticeable
distance btw 2 points.
Abbe's formula: omega = 0,61x(wavelength/nxsinomega)
color which the sum of them is the white light
phase contrast microscope - Correct Answers -Turns phase differences (to which the
eye is not sensitive) and converts them into amplitude differences which translate to
intensity differences
I = A2 (which the eye is sensitive to).
Useful for studying living cells, with no staining
Huygens-Fresnel principle. - Correct Answers -Every wave propagates so that each
point of its primary wavefront serve as a source of secondary wavelets (of small
amplitudes) that advance with the same speed and frequency as the primary wave.
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