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Z Old Biophysics I > Midterm II > Flashcards

Midterm II Flashcards

1
Q

What is Hooke’s Law?

A

F = -k * x

F is force, k is spring constant, x is displacement of spring at equilibrium

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2
Q

Define the accommodation power of the eye.

A

- the difference between the largest and smallest power of the eye

  • in other words: the difference between the power of the eye when focusing on the near point (shortest focal distance = highest power) and the far point (longest FD = lowest power)
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3
Q

What is the ‘normal value’ of the near point of vision in adults?

A

25 cm

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4
Q

How is the power of an eyeglass lens determined?

A

Dlens = Dcorrected - Duncorrected

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5
Q

What is used to designate the near point and far point in the equations for determining accommodation power or lens power?

A

Op is the near point, Or is the far point

they correspond to the nearest and farthest focal distances of the eye

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6
Q

What is normal sight called and what characteristics of the eye allow it?

A

Emmetropia

an elastic lens and normally round eyeball

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7
Q

What is the name of the condition when only close objects can be focused on?

What characteristics of the eye cause it?

What kind of lens corrects it?

A

Myopia or nearsightedness

  • caused by lengthening of the eyeball
  • divergent or negative lenses correct myopia
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8
Q

What is the name of the condition which only allows far objects to be in focus?

What characteristic of the eye causes it?

What kinds of lens corrects it?

A

**Hyperopia **or farsightedness

  • a **shortened **eyeball causes it
  • a convergent **(positive)** lens corrects hyperopia
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9
Q

What is the value of 1 radian?

And how many degrees is 1 radian?

A

2π

360 degrees

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10
Q

How many arc minutes is in one degree?

A

**60 arc minutes **per degree

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11
Q

What is the normal limiting angle of view in a healthy eye?

A

1 minute

or

0.0167 degrees

or

0.00029 radians

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12
Q

What is visual acuity? What else is it known as?

How is it calculated?

A
  • visual acuity is the resolving power of the eye
  • AKA visus
  • it is calculated as the ratio of the normal limiting angle (in minutes) to the actual limiting angle, in percents

visual acuity = 1’/⍺’ x 100%

(where alpha is the actual limiting angle in minutes)

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13
Q

What is the Maxwell Boltzmann distribution?

What parameters are graphed on its two axes?

How does an increase in temperature change this graph?

A
  • a probability distribution of particle speeds (or energies) in an ideal gas which shows that at a certain temperature, certain numbers of particles are likely to have certain energies
  • y-axis is probability or # of particles
  • x-axis is particle speed or energy
  • as temperature increases the peak of the curve lowers and moves rightward on the x axis, indicating more particles of high energy
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14
Q

What does the area under the curve of a Maxwell-Boltzmann distribution represent?

How does temperature affect it?

A
  • the area under the curve represents the total number of particles
  • temperature has no effect on this area, because it does not change the # of particles in the system
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15
Q

Define simple harmonic oscillation.

A

Oscillation with sinusoidal variation in which the restoring action is proportional to the deviation.

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16
Q

Define damped and undamped free oscillation.

A

undamped - oscillation without energy loss (e.g. due to friction) which is therefore constant

damped - oscillation with energy loss and decrease in amplitude over time

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17
Q

Define eigenfrequency.

How is it related to displacement? What determines it?

A

the frequency at which a free oscillatory system oscillates

  • independent of displacement
  • determined by characteristics of the system
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18
Q

What is critical damping?

How is the oscillation described in this case?

A
  • when energy lost per period is so large that the system reaches equilibrium without passing through the equilibrium point
  • oscillation here is aperiodic
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19
Q

What formula can be used to calculate minimum photon energy to create electron-positron pair?

A

E = 2mc2

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20
Q

What is damped driven oscillation?

What happens to frequency and amplitude over time with DDO?

A
  • oscillation with energy loss and an outside force acting on the system, replacing the energy loss
  • eventually frequency of system equals frequency of outside force, amplitude becomes constant
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21
Q

Define resonance in relation to oscillatory systems.

A
  • driven oscillation where otuside force’s frequency is close or equal to system’s eigenfrequency
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22
Q

What is on the x and y axis of a resonance curve?

A

Y axis - amplitude

X axis - frequency

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23
Q

Define the photoeffect.

How does the enrgy input relate to the energy output?

A

a gamma-photon removes any electron from the bound electrons of an atom by giving its complete energy to that electron

(kinetic energy of the removed electron equals nearly the incident photon energy)

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24
Q

Define Compton Scatter.

What MCQ from a past paper relates to this?

A
  • gamma photons remove “Compton electron” from outer shell of atom
  • Compton photon of lower energy is emitted
  • energy of gamma photon split between Comtpon e- and Compton photon

MCQ: During Compton Scatter…

A: …photons scatter on outer electrons of atoms.

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25
Q

Between what two states does a molecule go in phosphorescence?

A

Between non-excited singlet state (S0) and triplet state (T1)

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26
Q

What occurs in pair production?

A

A gamma photon of high enough energy is absorbed near the nucleus and an electron-positron pair is created

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27
Q

What occurs in scintillation?

A

an ionizing particle (beta particle) or high energy photon (X ray/gamma photon) causes a light flash in scintillator material which can be used to detect the particle/photon

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28
Q

What is Planck’s constant?

And what letter represents it in equations?

A
  1. 63 x 10-34J * s
    - represented by h

as in E = hf or h(c/λ)

29
Q

What is the formula for absorbance?

A

A = log J0/J

J0 is incident intensity, J is attenuated intensity

30
Q

What is the phase relationship between the exciting and produced photons in stimulated emission?

A

in stimulated emission, photons of the same phase as the exciting photons are produced

31
Q

How is population inversion maintained in the creation of laser light?

A

by external energy input

32
Q

What is a transition that does not produce electromagnetic radiation?

A

internal conversion

33
Q

In the spectrum of an x-ray source what determines the position of the spectral lines?

A

the material of the anode

34
Q

What kind of crystal was used in the scintillator for the nuclear medicine experiment?

A

a Thalium-doped Sodium Iodide crystal

NaI(Tl)

35
Q

Describe the basic layout of a scintillation detector.

What are its three main parts and their components? And the processes that take place in each?

A
  1. **Scintillator **- NaI (Tl) crystal, converts Ekin of electrons produced by in secondary processes to light scintillation via fluorescence of Tl in crystal
  2. **Photomultiplier **- semitransparent photocathode converts light from scintillator to e- flow via photoelectric effect, dynode array connected to +voltage multiplies e-s, anode collects e-s
  3. **Analyser/counter **
36
Q

Draw a scintillation detector set-up.

A
37
Q

What is secondary emission?

A

When a primary electron of high speed hits a metal surface (dynodes), several secondary electrons are emitted

38
Q

What does an integral discriminator do?

A

lets through only pulses above a certain amplitude in order to fliter out low amplitude noise

39
Q

Define luminescence.

A

Radiation that occurs due to the transition of an electron from an excited to a ground state

40
Q

What are the two categories of bonds and the bond types in each category?

A

Primary Bonds:

  1. Covalent - common electron state around participating nuclei
  2. **Metallic **- electromagnetism between conduction electrons and positively charged metal ions
  3. **Ionic **- Coulomb forces between ions

Secondary

  1. Van der Waals - btwn atoms without permanent dipole moment, temporary dipole interacts w apolar molecule and converts it to an induced dipole
  2. **H-bond **- H atom interbridges N, O or F
  3. hydrophobic interaction - weak Van der Waals
41
Q

What is Kasha’s Rule?

What does this mean for the emission wavelength?

A
  • photon emissions of appreciable yield only occur from the lowest excited state
  • emission wavelength is independent of excitation wavelength
42
Q

Describe the basic steps of the mechanism for atomic force microscopy.

A
  1. Van der Waals forces between the atoms of a sample and a very sharp probe tip on a cantilever bend the cantilever
  2. lasers projected onto the cantilever measure this bending
  3. the sample is scanned by moving the sample or the tip to cover the desired surface of the sample
43
Q

What are the 3 operating modes of atomic force microscopy?

A
  1. contact - tip touches surface of sample, cantilever deflection relates to surface topography (for soft biological samples)
  2. non-contact - tip is oscillated without contact to surface
  3. oscillating - cantilever is oscillated near its resonant frequency
44
Q

What are the properties of laser light?

A
  1. Low divergence (parallel beams)
  2. **Small spectral bandwidth **(monochromicity
  3. Large power
  4. Often polarized
  5. Possibility of extremely short pulses
  6. Coherence** **(waves with constante phase difference)
45
Q

What is the shape of water?

A

icosahedron

46
Q

What light phenomenon is responsible for the sky’s blueness?

A
  • red light is refracted more than blue, so more blue light reaches our eyes
47
Q

What does the velocity of an electron emitted from an alkali metal due to illumination depend on?

A

the wavelength of the illuminating light

48
Q

What interactions are important in determining protein structure?

A

covalent bonds

49
Q

What does the optimal integral discriminator setting on a scintillation counter yield?

A

the highest possible signal-to-noise ratio

50
Q

What does the optical resonator in a laser consist of?

A

two mirrors

51
Q

What does the Lambert-Beer law relate to? What variables does it take into account?

What is its equation?

A

the Lambert-Beer Law states that the absorption of a dilute solution is dependent on its concentration

  • includes concentration (c), sample thickness (x) and molar extinction coefficient (E-lambda) which depends on wavelength of applied light
  • the equation is log J0/J = E-lambda * C * x
52
Q

What are two other terms for absorbance?

A

optical density and extinction

53
Q

What does Abbe’s principle say about image formation in a microscope?

A

an image is formed only if at least the principle and first order maxima are captured by the objective lens

54
Q

What does the maximum point of the spectrum of luminescent radiation depend on?

A

the chemical quality of the emitting material

55
Q

During what state transition does fluorescence occur?

A

transition from excited singlet state (S1) to singlet ground state (S0)

56
Q

What kind of bonds bind the atoms WITHIN a water molecule?

A

covalent

57
Q

What is a light source that is not based on luminescence?

A

tungsten filament lamp

58
Q

What is stimulated emission induced by?

A

Spontaneously emitted photons

59
Q

Draw the optical resonator of a laser system.

A
60
Q

What else can luminescence be described as and why?

A

cold light - because unlike thermal radiation it does not involved the emission of heat

61
Q

Define Stokes Shift.

Represent it graphically.

A
  • the difference (wavelength or frequency units) between band maxima of absorption and emission spectra
  • in other words, the energy difference (which is lost via heat) between the absorbed and emitted photon
62
Q

What is stimulated emission?

A

the process by which an atomic electron (or an excited molecular state) interacting with an electromagnetic wave of a certain frequency may drop to a lower energy level, transferring its energy to that field

  • a photon created in this manner has the same phase, frequency, polarization, and direction of travel as the photons of the incident wave
63
Q

Draw the reduced eye model.

What is the refractice index (n) of the eye in this model?

And the distance between the nodal point and the retina, where the image is formed?

And the radius of curvature between the nodal point and the eye surface?

A

refractive index (n) = 1.34

distance K to retina = 17 mm

r = 5.1 mm

64
Q

How can eV be determined if given wavelength?

A

first use E = h * (C/λ) to determine energy in Joules

then use 1.6x10-19 Joules per eV conversion factor to get eV

65
Q

What are the letter designations of the electron shells starting from n=1?

A

n=1 is K, n=2 is L, n=3 is M and so one

66
Q

How can power density be determine mathematically if given the wattage of a laser and the diameter of its point?

A

Calculate the area of the point using πr2then divide the wattage by the area to get w/m2

67
Q

How can the number of photons of a certain wavelength emitted by a certain power of laser over a given time be calculated?

A
  1. Use P = ΔE/t to get total E in joules
  2. Find E of one photon using E = h*c/λ (with given wavelength)
  3. Divide total E by E of one photon
68
Q

How can the velocity of an electron accelerated by a certain voltage be calculated?

A
  • use Ekin = 1/2mv<strong>2</strong>rearranged to get velocity
  • use conversion factor of 1 eV = 1.6x10-19J to get E from voltage
  • mass of 1 e- in kg is 9.1x10-31kg
  • give answer in m/s
69
Q

How can wavelength of a certain matter wave be determined with only its velocity and mass?

A

Using the de Broglie equation

λ = h / m*v

Z Old Biophysics I (6 decks)

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