Lecture 2 Flashcards
1
Q
Refraction of Light
A
- light waves transmittedthrough a vacuum travel at a fixed velocity
- velocity is slowed through air,water , or glass
- EAch medium transmits light at acharacterisitc velocity
- Refractive index(R.I.)
- RI=Velocity of light/(velocity of light inside transmitting medium)
- Refractive index of air=1
- Refraction refers to then bending of light waves ,travel at a fixed velocity
- refracitve index is awlays greater then 1
2
Q
Does light bend when it travels through a medium?
A
- Yes light bends when it travels through a medium
- Degree of bending depends on
- R.I.
- Angle at which light strikes the surface
- Light waves follow the same path in either direction
- Note that light striking a perpendicular surface continues on through without bending
3
Q
What is refractive power
A
Refractive power is a meausre of how much a lens bends light waves. Measured in diopters
- 1 diopter=1 meter divided by the focal length of a lens
4
Q
Convex lens
A
Binding of all individual lights will converge at a single point at a certain distance past the lens
5
Q
Focal point
A
The point through which all parallel rays of light will pass after passing through each part of the lens
6
Q
Focal Length
A
- The distance from the center of the lens to the focal point
7
Q
Image formation and magnification by lenses
A
- Light waves traveling through a convex lens will converge at a focal point
- a real image is formed when the object is placed outside the focal point
- Real image is inverted
- Real image can be projected onto a screen
- Real image differs in size from the object
- greatest magnification will be obtained from lenses having a very short focal length with the object as close as possible to the focal point
- how much it varies depends where it is in relationship to the focal point
- Convext lens will create real image if hte object is outside the focal point
8
Q
When is a virtual image formed
A
Virtual image is formed when the object is placed insdie the focal point
- Virtula image is not inverted
- virtual image cannot be projected onto a screen virtual image can be magnified
- no points exist at any plane in space at which rays radiating from the objects are brought to a focus
- rays radiate outward and do not form a real image when object is inside focal point
- when you look at a mirror its a virtual image
9
Q
Resolution
A
- ability of a microscope(or any optical instrument) to distinguish two small points as separate points
- To accomplish this, the diamter of diffraction lines around the points must be reduced
- Resolution is important to be able to see objects
- Resolving power is how close two objects be and still be seen as seperate objecs
- when light waves strike an object as they go off the edge of the object will raidate and wavelengths will mi and be seen as one blurry object if we don’t have high resolution to seperate wavelengths
10
Q
What is the resolution equation
A
- d=.61(lambda)/(nsina)
- lambda=wavelength of light(3800A)
- .61=constant relating to defined overlap allowed for two points to be recognized as separate by a human observer
- n=refractive index of medium surrounding object
- sin a= angle of cone of light entering objective lens(max 180)
- n sina=numerical aperture
- Max=1.4
- D actual distance that two objects can be seen as separate things
- Want D to be smaller becasue it means that the objects can be closer together and still be seen as sepearate objects
- Light microscope never gets a NA of above 1.25 usually
11
Q
Resolution in light and TEM microscope?
A
- light microscope the highest resolution is about .5um
- In TEM the highest is theoretically .01 angstorms, but the actual resolution achievable is 5-10 angstorms(=.5-1.0nm)
- Don’t see the .01 angstorms becasue electrons have a defraction pattern and create sometimes blurry images at lower and lower resolutions
12
Q
Compound optical(light) microscope
A
- Also referred to as birght field microscope
- Direct descendent of the microscopes used in 1800s
- Components
- Light sources
- Condenser
- Stage
- objective lens
- Ocular lens
- Good microscope is made up of seperate lenses glued together to create a better resolution
- Objective lens has a rotating ability to chagne the magnification
- stage where all the action happens
- Condenser -to create optimal cone of light that will pass throuh the objective lens and very detailed instruction on how to set condenser,creating cone of light that is consistent with the objective lens
13
Q
Pros and cons of the Light Microscope
A
- Ability to magnify
- Ability to resolve strucutural detail
- Specimen must be thin
- Relatively little contrast in the unstained specimen
- Important thing is the resoltuion not the magnification
- Specimen must be thin is a con because it takes a lot of work to get a specimen thin enough , and there is a little contrast in a non stained specimen
14
Q
Phase contrast microscope
A
- Converts phase shifts(invisible to the eye) in light passing through a transparent specimen to brightness changes(visible to the eye) in the image
- Can be used to examine unstained cells and tissues
- Useful for examination of living cells
- Different parts of a cell have small differences in the refractive index
- Light passing through these regions become deflected and out of phase with the main stream of light waves
- Out of phase wavelengths are matched with other induced out of phase wavelengths which cnacels their amplitude
- Creates light waves that can be seen in contrast to other light waves that have not been retarded
- Phase contrast chagnes the phase into patterns of darkness and light
- The condenser system is special and doesn’t allow light to pass directly through the specimen which allows for the light to hit specimen at different angles
15
Q
Fluorescence Microscope
A
- Detects molecules that emit light of wavelengths in the visible range when exposed to a UV light source
- Detects naturally occurring fluorescent(autofluorescent) molecuels such as Vitamin A
- Most widespread application is to detect induced fluorescence:
- Detection of antigens or antibodies in immunochemical staining procedures
- detection of fluorescent tracers injected into animals or cells
