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Biophysics I > Microscopy > Flashcards

Microscopy Flashcards

1
Q

Image formation on a curved surface

A
  • Lenses are curved surfaces.
  • If light rays meet, they form an image.
  • Angle of refraction depends on refractive index of lens.
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2
Q

Principal light rays

A
  • Parallel ray: Parallel to optical axis
  • Central ray: Passes through center of curvature.
  • Focal ray: Passes through focal point
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3
Q

Lens combinations

A
  • Lenses are combined in a compound microscope. (Eyepiece and objective)
  • Image magnification can be manipulated by changing distance between the lens and specimen and distance between 2 lenses.
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4
Q

Refractive power

A

Degree to which a lens is able to converge or diverge light.
D = 1 / f

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5
Q

Lens equation

A

D = 1/f = 1/i + 1/o

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6
Q

Image formation by the light microscope

A

Diagram with object, objective and eyepiece lenses, images, and eye.

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7
Q

Rules of image formation

A

Diagrams with F, 2F (Real/virtual, Upright/inverted,…)

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8
Q

Concepts of magnification and angular magnification

A
  • Magnification is I/O size.
  • Angular magnification is tanB/tanA
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9
Q

Magnification in the light microscope

A

M = I / O = i / o

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10
Q

Oscillations

A

Movement back and forth around an equilibrium.

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11
Q

Diffraction on an optical grating

A
  • Optical grating: Large number of closely spaced slits.
  • A structure with periodic optical properties separate light of different wavelengths and refracts them at different angles.
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12
Q

Polarization of light

A

Unpolarized light (electric field vector can be found in any plane that contains direction of propagation) becomes polarized light (electric field vector only in 1 plane) by an optical filter

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13
Q

Types of waves

A

Wave is a disturbance that carries energy.
- Transverse waves: Direction of oscillation is perpendicular to direction of propagation, Electromagnetic waves, vacuum.
- Longitudinal waves: Direction of oscillation is parallel to direction of propagation, Sound, requires a medium.
- Matter wave: e.g. electrons

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14
Q

Limit of resolution of the light microscope

A
  • Smallest noticeable distance between 2 points.
  • Abbe’s formula: = 0.61 * wav/nsinw (image forms in microscope only if at least first order maxima enters the objective lens)
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15
Q

Phase contrast microscope

A

Turns phase differences and converts them to amplitude differences, therefore intensity differences which can then be detected by the eye. (For studying live unstained cells)

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16
Q

Huygens-Fresnel principle

A

Every wave propagates so that every point of its primary wavefront serves as a source of secondary wavelets advancing with same speed and frequency of primary wave.

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17
Q

Polarization microscope

A
  • Makes brief ringing details of specimen visible. (Cell membrane, striated muscles,…)
  • Microscope has polarizer, illuminates specimen with linearly polarized light.
  • Other side of specimen has analyzer at 90deg. From polarizer, at this angle view is dark.
  • Only light that was rotated by birefringent parts of specimen pass, so only these details are visible.
18
Q

Wave diffraction

A

When light passes through a slit which is near the size of the wavelength, it spreads around the slit. Ties to Huygen’s principle explaining diffraction pattern.

19
Q

Interpretation of the color of light

A
  • Colors can be separated by wavelength.
  • In our eyes, we have cells which can sense different frequency of light.
20
Q

Wave interference

A
  • Constructive interference: Same phase (crest meets crest)
  • Destructive interference: Opposite phases (crest meets trough)
21
Q

Wave nature of light

A

Phenomena which prove wave nature of light:
- Diffraction
- Interference
- Polarization

22
Q

Dual nature of light

A
  • Can behave like a wave
  • Can behave as matter (photoelectric effect) energy packed in quanta depending on frequency.
23
Q

Matter waves

A
  • Matter can exhibit wave-like properties
  • De-broglie’s hypothesis: Wavelength = Plank’s constant / Momentum (m*v)
  • (Davisson-Germer experiment proved that electrons scattered formed diffraction patters)
24
Q

The electromagnetic spectrum

A

Entire distribution of electromagnetic radiation according to frequency or wavelength, and their respective photon energies.

25
Q

The photoelectric effect

A
  • E = hf
  • When a photon delivers enough energy to an electron causing it to leave the atom.
  • Proves quantized nature of light (photon) and thus the particle nature off light.
  • Einstein
26
Q

The electron microscope

A
  • Small wavelength of electron allows for much higher resolution in EM.
  • TEM: Uses electrons passing through the sample to create an image.
  • SEM: Creates image by detecting reflected/knocked-off electrons.
  • Electron gun (tungsten filament), High voltage for acceleration of electrons, condenser, electromagnetic lenses.
27
Q

Photon energy, the eV scale

A
  • E = hf
  • Covert to eV by dividing by charge of electron, 1.6 x 10^-19
  • The amount of K.E in an electron that is accelerated in an electric field of 1 volt.
28
Q

Interpretation of momentum of light: optical tweezers

A
  • Photon Momentum = h / wavelength
  • Optical tweezers: utilize the photon momentum to trap/control the movement of very small objects.
29
Q

Models of the atom (Dalton, Thomson, Rutherford)

A
  • Dalton: Showed that matter was made of indivisible particles (atoms) which can not be broken down further.
  • Thompson: Discovered that atoms have electrons which were stuck throughout the positively charged substance.
  • Rutherford: Showed that all positive charge was in the middle (nucleus)
    (Rutherford and Chadwick discovered protons and neutrons)
30
Q

Wave nature of the electron

A
  • Electrons behave like waves in certain situations (diffraction)
  • Wavelength calculated = h / momentum
  • Davisson Germer experiment.
31
Q

The bound electron, quantum numbers

A
  • Principal QN (n): Size of atom, from shells. (1, 2, 3,…)
  • Azimuthal QN (l): Shape (0, 1, 2,…)
  • Magnetic QN (ml): Orientation (-l,… , l)
  • Spin QN (ms): Spin (-1/2, 1/2)
32
Q

Bohr’s atomic model

A

Electrons in an atom can only occupy certain distinct orbits around the nucleus.

33
Q

Heisenberg’s uncertainty principle

A
  • One cannot know all parameters describing a particle at a given time.
  • E.g. when momentum is calculated, there is more uncertainty about its location.
  • Due to wave nature of particles.
  • We cant know position and speed of a particle.
34
Q

Physical foundations of the periodic table

A
  • Numbered according to increasing atomic number/Proton number
  • Size increases down a group, and decreases across a period.
  • Every group number has the same number of valence electrons.
  • Ionization energy increases across a period, and decreases down a group.
  • s, p, d,… blocks
35
Q

Franck-Hertz experiment

A
  • To prove Bohr’s atomic model stating that electrons exist in quantised state within the atom.
  • Tube filled with Hg, electron emitting cathode, grid, and anode.
  • In order to interact with Hg atoms, a specific amount of energy had to be given to the electrons by voltage.
  • Measuring current at end of tube makes it possible to measure how much energy went to atoms, and how much was left over.
36
Q

Potential energy of interatomic interactions

A
  • Atoms in a molecule are organized in fixed positions in which the molecule stores the least potential energy.
  • Most stable form
  • P.E = E attraction + E repulsion
37
Q

Electronegativity

A
  • Strength of which an atom can hold onto its electrons and ionize other atoms.
  • Smaller atoms with high atomic number are more electronegative.
  • Fluorine is most electronegative.
  • Higher electronegativity atoms pull electrons towards them (causing polarity in molecules)
38
Q

Scanning probe microscopy

A
  • Can form an image of an atomic size object by detecting various interactions depending on probe.
  • Atomic force microscope (AFM) measures van der waals force between probe and sample.
  • Probe connected to cantilever, laser beam.
  • Measures change in position of cantilever
39
Q

Primary and secondary bonds

A
  • Primary bonds: Covalent, Ionic, Metallic
  • Secondary bonds: Dipole, Van Der Waals, hydrogen bonds
40
Q

Resolving power of the atomic force microscope.​

A
  • Resolution fractions of a nanometer.
  • Allows the study of strength and length off chemical bonds and the detail of molecular structure.

Biophysics I (7 decks)

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