Quiz 1 Flashcards
1
Q
What are the properties of light?
A
1) light carries electric and magnetic fields
2) Light has a frequency, wavelength, momentum and carries energy
3) Light can have a polarization
4) Light has coherence meaning it can be in or out of phase for constructive or destructive interference
5) Light is a particle. Photons can interact with other photons, gravity and have mass
6) Photons are bosons meaning more than one photon can occupy a given state
2
Q
What formulas specify energy, momentum and wavelength of light?
A
3
Q
What is the classical electromagnetic theory? What formula does it represent?
A
The classical electromagnetic theory is represented by the Lorentz force, which is the force of a particle moving through an electromagnetic field.
4
Q
What is Gauss’s law of electric charges?
A
Describes the generation of an electric field by a single charge.
5
Q
What is Gauss’s law of magnetism?
A
Describes the generation of a magnetic field by magnetic dipoles. No single-point charges.
6
Q
What is Faraday’s law?
A
Describes how a moving electric field can generate a magnetic field.
7
Q
What is ampere’s law?
A
Describes the creation of a magnetic field by electric currents and/or moving electric fields.
8
Q
How can classical electromagnetic theory describe light?
A
It is one of four forces in nature (gravity, weak, EM, strong). Light is self-propagating because it is the composite of two waves varying in unison (electric and magnetic). There are two main acting forces in EM theory –> electrostatic forces and magnetic forces
9
Q
What are ways light can be generated?
A
1) from a heat source such as thermal or radiation
2) from the emission spectrum of translucent matter interacting with a specific spectrum
10
Q
What is black body radiation?
A
It is also known as thermal radiation and is emitted by all objects with temperatures above 0K.
11
Q
How do you calculate net radiative heat loss?
A
12
Q
What makes lasers different than normal light sources?
A
Laser light is directional, coherent, monochromatic and polarized.
13
Q
What thermal effects may lead to energy loss?
A
Conduction, convection, radiation
14
Q
How do you calculate the total energy radiated by a body?
A
E = (P)(t)
15
Q
How is light generated?
A
When electrons are excited to a higher energy level through a different process, when the electrons are excited and fall back to a relaxed state they release photons and light is produced.
16
Q
What is stimulated decay?
A
This implies a catalyst incident photon triggers the emission of a second photon from an atom.
17
Q
How do you calculate exponential decay?
A
18
Q
What is mean lifetime and how is it calculated?
A
19
Q
What is fluorescence?
A
It is a property in which a compound can absorb light of a specific wavelength and emits a different wavelength of light. Typically has a shorter mean lifetime or half-life.
20
Q
What is phosphorescence?
A
It is similar to fluorescence; however, the material does not immediately re-emit the absorbed radiation. The transition from excited state to ground state happens much slower and the light re-emitted has a lower intensity.
21
Q
What is photoluminescence?
A
It is the emission of light by the absorption of another photon. This process is known as stimulated emission!
22
Q
What is chemiluminescence and how is it related to bioluminescence?
A
Chemiluminescence is the emission of light by a chemical reaction. Bioluminescence is a type of chemiluminescence as it involves the reaction in which ATP drives the oxidation of optical molecule luciferin with the help of enzyme luciferase to form oxyluciferin and light. The excited state of luciferin will emit of a photon.
23
Q
How do you calculate the quantum yield?
A
24
Q
What is Rayleigh scattering?
A
It is elastic scattering on objects with smaller wavelengths than the incident light.
25
What is Mie scattering? What calculations are associated with it?
It is also elastic scattering, however the objects are similar in size as the incident wavelength.
26
What is elastic scattering?
the interaction between the object and light does not involve any energy transfer.
27
What is raman scattering?
It is inelastic scattering which means there is an energy exchange when light is in contact with the object. This results in polarization change in the molecules being hit by light. The energy of the scattered photon does match that of the incident one.
28
What is the difference between chemiluminescence, fluorescence and phosphorescence?
Fluorescence and phosphorescence are similar in that they both absorb light of a specific wavelength and emit one with a different one. However, phosphorescence there is a delay in light emission the intensity is a lot.
On the other hand, chemiluminescence requires a chemical reaction (input of energy such as ATP) to produce light.
29
What is the main difference between bioluminescence and thermal radiation?
Bioluminescence generate light by a chemical reaction whereas thermal radiation generated by heat.
30
What evelutionary pressures drive bioluminescence?
Survival and reporduction
31
What is the photoelectric effect?
It is the emission of electrons when electromagnetic radiation such as light hits a material. These elctrons are called photoelectrons.
32
Recognize wave equations
33
Describe the huygens-fresnel principle
when light interacts with a material at an interface each point of interaction is a source from new spherical waves which creates a wave front.
34
What is fermat's principle?
Light always travels the path of shortest time not distance.
35
Know snell's law equation
36
What is total internal reflection? How do you calculate the critical angle?
It implies that there is no refraction of light because it is entering a medium that is less dense causing the incident beam to be completely reflected.
37
What is Brewster's angle and how do you calculate it?
It occurs when the angle between the reflected and refracted rays are 90 degrees. The reflected rays will be polarized, and the refracted rays will only be partially polarized.
38
What are the purposes of pinholes and irises and what is the pinhole effect?
pinholes control the amount and plane of light passing through to the system. The pinhole effect suggests that the smaller the pupil size, the less defocus from spherical aberrations there are. This is because all unfocused rays are blocked leaving only focused light to land on the retinal and control a clear image.
39
What is the difference between dielectric mirrors and metallic mirrors?
dielectric mirrors have a thin layer of oil, water or air so that light can interfere with itself either constructively to destructively. Mettalix mirrors are made of silver and aluminium and the percentage
40
What are beam splitters?
They are used to divide an incident beam into two separate beams. One is reflected and the other is transmitted.
41
What do filters do? What types of filters are there? (hint: there are 6!)
Filters control the intensity of light and its spectral characteristics.
Neutral density filters = change the intensity of light, but not the wavelength.
Bandpass filters = only allow a specific range of wavelengths through (they let a specific band pass).
Edge filters = allow only long wavelength or short wavelength light to pass, depending on the type (long-pass or short-pass).
Dichroic filters = only allow a very small range of wavelengths to pass. They are similar to bandpass filters.
Notch filters (also referred to as bandstop filters) = let all wavelengths through except those within a specific range.
Diffusers = make the incoming beam of light less abrasive, less intense and more ambient overall. These are often used in photography studios, for example, to properly light a subject!
42
What do lenses do?
They convert planar waves into circular waves to focus light on a specific point or scatter light away from a specific point.
43
What is the lens maker's equation (1)?
44
What is the lens maker's equation (2)?
45
What do prisms do?
Made of at least two flat surfaces with a difference in angle. They disperse, split or reflect light into various polarizations or wavelengths. They work because different colours travel at different speeds.
46
What are gratings and how do they work?
It is an element that disperses light composed of different wavelengths into light components by wavelength. When white light enters a grating, the light components are diffracted at angles that are determined by respective wavelengths.
47
What equations are associated with gratings?
48
What is polarization?
It applies to transverse waves and specifies the geometrical orientation of the oscillations.
In a transverse wave the direction of oscillations is perpendicular to the direction of motion of the wave. In linear polarizations the fields oscillate in a single single direction.
49
How do optical fibers work? What formula represents the incident angle?
They operate by total internal reflection.
The internal material must have a larger index compared to the cladding (material that wraps glass)
50
What is optical coherence tomography?
OCT uses mirrors, lenses and beam splitters and optical fibers and filters to measure the amount of ballistic photons passed through a tissue and creates a medical image/
51
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53
54
What is the difference between double convex and double concave lenses?
A) double convex lenses are converging lenses which focus light. The image can be located on either side of the lens. A virtual image can be upright or flipped and the virtual image can be bigger or smaller
B) double convex lenses are diverging light that scatters light. The image is always located on the object side of the lense and is always virtual, upright and reduced in size.
55
What is the lens equation and magnification equation?
56
Know the lens sign conventions
+ Focal length = double convex
- Focal length = double concave
+ image distance = real image
- image distance = virtual image
+ height = upright virtual image
- height = inverted real image
57
What is the lens makers equation?
58
What are compound lenses?
lens made of simple lenses mounted on a common axis usually in close juxtaposition.
59
What is structural colouration
It is a mechanism in which an biological structure has a specific grating pattern which leads to constructive and destructive interference of light which distates the colours reflected.
60
What cells do cephalopod camouflage contain?
1) chromatophores = elastic sacs of pigment whose expansion and contractions are controlled by muscles making them more or less visible
2) iridophores = stacks of cells that reflect light at different wavelengths
3) leucophores = scatter the full spectrum of light allowing them to appear white
61
62
63
64
Position 6 is at the focal point
● When an object is placed on the focal point, no images are produced (virtual or real)
● This is because the refracted rays neither converge or diverge
● After refracting, the light rays are travelling parallel to each other and cannot produce an image
65
66
What is beer-lambert's law?
Describes the of which absorption occurs based on the material light is interaction with.
67
What is the formula for absorbance and scattering coefficients, what are they both defined by?
They are both defined by the cross-sectional area of the material which is interacting with light.
68
What is transmittance? How do we calculate it for both absorption and scattering?
It is the measure of how much light from a light source is able to pass through a material to the other side. How much light is not being scattered or absorbed.
69
What is the mean free path?
It is the average distance over which a moving particle travels before changing its direction or energy as a result of collisions with other particles. The greater the path the greater the penetration the deeper the imaging. It depends on refractive index variations, size of scatter and wavelength.
70
What is the biological optical window?
The near-infrared window defines the range of wavelengths from 650 to 1350 nanometre where light has its maximum depth of penetration in tissue. Within the NIR window, scattering is the most dominant light-tissue interaction, and therefore the propagating light becomes diffused rapidly.
71
How can we use the interaction with light and tissue as an engineer?
72
Q1: Why can’t we use light in the
visible range for deep tissue
penetration? Which wavelengths
of light can be used?
73
Give a summary of photosynthesis:
Photosynthesis converts carbon dioxide from the air and water from the soil into sugar and oxygen.
74
What is the difference between photosynthesis and cellular respiration?
Photosynthesis: captures energy from sunlight to produce sugar and oxygen. It only occurs in plants and autotrophs and in the cell's chloroplasts.
Cellular respiration captures energy from sugars and releases energy. It occurs in all eukaryotes and also in autotrophs, and heterotrophs and takes place in the mitochondria.
75
Where do the light dependant reactions take place and what do they produce?
Occurs in the thylakoid membrane which is located in the stoma of the chlorosplast. The electron transport chain produces ATP, NADPH and O2.
76
Describe PSI (700) and PSII (680)
there is a complex of chlorophyil molecules which make up the antenna region. The molecules are excited by light and transfer an excited electron to the reaction center complex which transfer them to the electron transport chain.
77
Describe the electron transport chain
Excited electrons travel down, continuously reducing the molecule to a lower level which produces H+ ions and NADPH. The hydrogen ion gradient which allows atp synthase to drive the reduction of ADP and pi to ATP. The hydrogen gradient is in the lumen.
78
What is the difference between light dependant and dark reactions?
Light: occurs in light. The reactions are H20 and the products are ATP and NADPH. It is used to convert light energy to chemical energy
Dark: the calvin cycle uses the energy (ATP) from light to convert CO2 into sugar by carbon fixation. Reactants are CO2, ATP and NADPH.
79
What is artificial photosynthesis and what are the advantages and disadvantages?
It is a carbon neurtral sustainable way of generated energy by splitting water to form molecular hydrogen/ Photocatalytic water splitting can be achieved by photon-coupled multi-electron transfer processes.
Advantages: solar energy can be immediately converted and stored and the by-products are APS and carbon neutral.
Disadvantages: materials often corrode in water and are less stable. The cost is not advantageous enough.
80
What do rod, cones and opsins do?
Rod photoreceptor cells handle light intensity detection
● Cone photoreceptor cells handle colour vision
● Opsins are light-sensitive protein in the photoreceptor cells. Retinal is one such
protein.
● When light is absorbed by retinal it transforms into an activated version of itself.
● This is called photoisomerization, as light (“photo”) triggers a change in
molecular configuration (“isomerization”).
81
What is phototransduction?
Process in which light detected photoreceptors cells are converted to electrical impulses before these impulses are sent to the brain.
82
Describe the overall visual process:
83
What is coulomb's law and what is the formula?
Quantifies the electrostatic force between charged particles.
84
What is coulomb's law and what is the formula?
Quantifies the electrostatic force between charged particles.
85
Difference between intra and inter molecular forces?
Iconic? Covalent (non-polar, polar)? Metallic?
Intra - occur between atoms of the same molecule
Inter - between atoms of different molecules
Ionic: bonding occurs between a metal and a non-metal element. Valence electrons are completely transferred due to an electronegativity difference.
Covalent: between two non-metals and is a sharing of electron. Non-polar requires a small electronegativity difference whereas a polar bond requires a larger but still small range which creates a charge imbalance
Metallic: covalent bonds that occur between metallic elements. The atoms are tightly packed in lattice structure. There are fixed positive charged metal ions and free valence electrons
86
What is the Lennard Jones potential and what is the formula?
Describes the potential energy between non-bonding atoms given the distance between the. The potential rather than the potential energy is computed
87
Lenard Jones formula
88
Describe the Lennard-jones potential:
The Lennard-Jones potential is a function of the distance between the centers of two particles. When two non-bonding particles are an infinite distance apart, the possibility of them coming together and interacting is minimal. For simplicity's sake, their bonding potential energy is considered zero. However, as the distance of separation decreases, the probability of interaction increases. The particles come closer together until they reach a region of separation where the two particles become bound; their bonding potential energy decreases from zero to a negative quantity. While the particles are bound, the distance between their centers continue to decrease until the particles reach an equilibrium, specified by the separation distance at which the minimum potential energy is reached.
89
What does the larger repulsive term, smaller repulsive attrative terms and sigma value represent?
larger repulsive term = London dispersion force
smaller repulsive attrative terms = LDF
sigma value = how close the particles can get to each other
90
Describe disulphide bonding
Covalent bond derived from the oxidation of two thiol (S-H) groups. Occurs intramolecularly and intermolecularly.
91
Describe capillary action
It occurs due to adhesion of water molecules to the sides of the container and cohesion, the attraction of molecules to one another.
92
Describe surface tension
results from the cohesive forces between liquid molecules at an interface. It causes surface film.
93
What do surfactants do?
They are compounds that lower the surface tension by disrupting intermolecular forces. They are amphiphilic molecules.
93
What do surfactants do?
They are compounds that lower the surface tension by disrupting intermolecular forces. They are amphiphilic molecules.
94
What is self-assembly and what are the forces responsible for self-assembly?
It is a process in which a disordered system of pre-existing components form an organized structure pattern.
Electrostatic intramolecular and intermolecular interactions (mostly H-bond) and external forces such as electric, magnetic, flow, osmotic, and gravity.
95
What is spontaneous self-assembly and what formulas help explain it?
It is a spontaneous process that releases free energy.
G < 0 and there must be a gain in entropy S > 0
96
Describe the hydrophobic effect
Due to hydrophobicity which is the result of entropy and is often a major contributor to self assembly. When you add non-polar molecules in water there is a distribution of hydrogen bonding network between the two molecules. The non polar groups aggregate and the hydrogen molecule orient on the outside to minimize disruption. This results in a an increase in entropy due to restricted mobility.
97
What are examples of self-assembly in nature
Lipid molecules forming oil droplets in water
● Polypeptides folding to form a functional protein
● The way RNA and ribosomal proteins combine to form a functional
ribosome
● Formation of crystalline structure
● Formation of the lipid bilayer
98
What systems utilize the
hydrophobic effect (natural and
artificial)?
Amphiphiles
○ Molecules that contain both hydrophobic and hydrophilic sections
○ Detergents, cellular membrane, etc.
● Protein folding
○ Hydrophobic regions fold inward
● Protein purification
○ Proteins can be separated based on their hydrophobicity
99
How are cones and rods
distributed on the retina? How is
this related to the blindspot?
Fovea: a small depression at the center of the retina where visual acuity is
the highest. Only cones are located at this point.
Blindspot: Location where optic nerve passes through retina; no rod or cone cells.
100
What is superhydrophobicity?
It is the result of micro and even nano-structured patterns. Hierarchical structures increase hydrophobicity which makes it easier for water to flow on a material.
The more hydrophobic the surface the greater the greater its contact angle will be
superhydrophobicity = angle > 90
101
How do you quantify hydrophobicity?
102
What is wenzel regime and cassie-baxter regime?
Wenzel: micro-structures in which water droplets embed themselves in the spaces
Baxter: hierarchical nanostructures that water floats on
103
What are networks?
They are combinations of various nodes that are linked together through edges.
104
What are some applications of superhydrophobic surfaces?
1. oil water separation
2. self-cleaning materials
3. anti-corrosion
105
List the types of channel proteins a membrane can have
106
What are action potentials, neurotransmitters and sensory neurons?
Action potential: Voltage-sensitive channels in neurons and open and close in response to the voltage across the membrane.
● Neurotransmitters: Ligand-gated channels open and close in response to the binding of a ligand molecule.
● Sensory Neurons: Ion channels open and close in response to other stimuli, such as light, temperature or pressure.
107
What are the properties of an electric circuit?
108
What are the components of an electrical circuit?
Battery: converts chemical energy into electrical energy via an electrochemical oxidation-reduction reaction
Resistor: implements electrical resistance used to reduce the current flow, divide voltages and adjust signals
Capacitors: electrical component that stores electrical energy in an electric field.
109
Describe the Hodgkin-Huxley model:
Uses conductance to describe how action potentials are initiated and propagated
The lipid bilayer is the capacitance
Voltage-gated and leak ion channels are non linear and linear resistors
Electrochemical gradients are the batteries because they drive the movement of ions
Ion pumps and exchangers are current sources
110
What is the nernst potential
the reversal potential of an ion is the membrane potential at which there is no net flow of that particular ion from one side of the membrane
111
Draw the Hodgkin-Huxley circuit and equations for the current through the lipid bilayer, ion channel currents and total current.
112
Write out the nernst and goldman equation
113
What are semiconductors?
Elements with 4 electrons in their valence shells which allows them to create 4 bonds with their neighbours creating a stable lattice. This makes it hard for electrons to move around so its hard for electricity to flow through these resistors.
114
Why is the membrane similar to N-P junctions
In the “N-doped” area, group 5 elements are added in small quantities. The single fifth electron will be mobile in the system. In the “P-doped” area, group 3 elements are added in small quantities. The “gap” left by the mission valence electron will lead to current generation when free electrons from the N-doped region migrate to the P-doped region. Overall, a junction potential is created, much like the potential generated in the case of the plasma membrane!
115
What is doping?
It involves introducing impurities to the pure lattice structure. The n-type includes 5 valence electrons, one free election is left which can move around the lattice creating a current. in the p-type there are 3 valence electrons so one free whole. the whole can move across the lattice too creating a current.
116
How are values for ion
concentration experimentally
obtained?
117
Explain why the lipid bilayer can be modelled as a
capacitor
A capacitator is made of two conducting surfaces separated by an insilator used to store charges. The lipid bilayer has outlet layers of polar heads separated by non polar tail region which separates the intracellular and extracellular matrices
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