Week 2 Flashcards
what happens to radiant energy (light) when it passes through an object
-it is reflected, absorbed and transmitted
-signal is directly or inversely proportional to analyte concentration
what is constructive interference
-when two waves go through the same point they interact constructively or destructively
-when crest and trough are in phase with same frequency get added together to produce a wave with large amplitude and intensity
-the 2 short waves get added to make one tall wave
what is destructive interference
-when two waves that are not in the same phase interact with each other producing smaller amplitude with low intensity or a flat like
-this is used to isolate light from specific wavelength
what is light
-both wave and particle
-a wave because it can move in space like a wave
-a particle because it is a stream of particles made up of photons with no mass or charge moving at speed of light. The energy the photon carries varies with color
-energy known as electromagnetic radiation. Maxwells electromagnetic theory mentions that light is energy in waves with electrical and magnetic fields
What is the visible light spectrum?
-400 (violet) to 700 (red) nm
-gamma, xray, UV, THEN Visible
how do you select the appropriate wavelength to measure absorption
-chose a wavelength with the greatest sensitivity. So one with the max difference in Absopr readings with a small concentration change
-the wavelength chosen has to show a broad peak so if there is a slight error in calibration it will not create a large change in absorbance and loss of sensitivity
-a wavelength selector isolates the wavelength for measurement
-it seperates the light emitted from the lamp into its colors and isolates the wavelength you need .
-you want high intensity of the wavelength you need and low transmission of other ones
what is amplitude and cycle
Amplitude:
-wave height
-determines intensity of light which is also determined by the light source which must emit a constant source
Cycle
-one wave made up of one crest and one trough
=cps = CYCLES PER SECOND
what is frequency F or v
-number of waves/cycles per second that pass a point in one second
-constant no matter the medium
-controlled by light source
-Hertz HZ
-frequency and wavelength are inversely proportional so f=1/lamda. so if one increases the other decreases.
-wavelength = speed of light (c)/ frequency
Velocity (c)
-how fast an object moves through space (m/s)
-in a constant vacuum speed travels in a straight line
–related to wavelength and frequency
-dependent on media - slow in dense media
-shorter wavelengths have lower velocity
c=wavelength x f
what is Energy
-directly proportional to frequency and inversely proportional to wavelength
E=hf E - hc/lamba
h is Planks constant = relationship between energy and frequency
for example
Violet light - shorter wave, high f = high E
Red light -longer wave, low f = low E
What is reflection and what are the types of surfaces
-when light is returned from an illuminated surface which is not the source of light
-the angle of incidence = angle of reflection
-Vitros 350 measures reflected light
Smooth surface like a mirror
-when light is reflected it is in equal angle perpendicular to the surface called specular reflection
-makes an identifiable image
Rough surface
-light is scattered/diffused
-makes unidentifiable image
-The amount of light and its reflection is dependent on the nature of reflecting body and the shape and nature of the reflecting surfacew
what is refraction
-light bending between two different medias. When light passes from one to an another - air into glass, air into water
-Speed of light varies based on nature of the medium and the wavelength of light
-Refractometers are used to measure RI which indirectly measures total dissolved solids
Formula for refraction (n)
-the amount light bending between two media is dependent on the RI
-it is the ratio of velocity of light (c) in a vacuum vs velocity of light in the medium (v)
n=c/v n>1
-light entering a dense medium (air to water) will bend toward normal so the angle of refraction is less than the angle of incidence
-light entering a less dense medium (water to air), the ray is refracted away from normal making the angle of refraction greater then the angle of incidence
-velocity decreases in a denser medium
what is the dispersion of light
-when white light is spread into a full spectrum after passing through a prism - nonlinear
-as the white light seperates into different colors the associated wavelengths travel with a different velocities and refract at varying degrees
-shorter wavelength = smaller angle of refraction entering the prism and greater angle of refraction of light coming out of the prism ?
what is the diffraction of light
-how light bends around corners and obstables
-diffraction varies with wavelength - shorter waves bend less
-causing constructive and destructive interference
-diffraction gratings disperse white light into different wavelengths
how does diffraction grating work and what are the types
-ruled, reflective surface disperse polychromatic light into a uniform spectrum
-light is dispersed into colors using diffraction and wave interference
2 types are reflectance and transmittance
simple spec: wavelength is changed by pivoting the grating
-angle of the grating to the fixed exit slit causes different wavelengths of light to pass through the slit
what are the advantages of diffraction grating
-linear dispersion
-can produce less than 1nm of light in some analyzer
-better than prisms for isolation
what does the absorption of light depend on
-chemical structure of molecules in sample
-concentration of light absorbing molecules
-wavelength of light passing through the sample
what is absorption
-when white light passes through a colored solution some is
1.absorbed selectively by molecules in the solution
2. and rest is transmitted (these wavelengths are seen as color)
-blue solution absorbs yellow transmitting wavelength to appear blue (both complementary colors)
-ref absorbs green and transmits red
what is transmittance
-light traveling through a substance
-any light that is not transmitted is absorbed
-ratio of radiant energy transmitted through a medium divided by radiant energy shined on the medium
T= I/I0
-there are no units so T is expressed as % T of a 100
what is the relationship between A and %T
100%T= 0 absorbance
-100%T is set with a blank reagent with all reagents but not the specimen
-as A increases, %T decreases, therefore A and T are inversely related. They are inversely and logarithmically related A=2-log%T
-on LINEAR graph paper %T is inversely proportional to concentration
what is Beers law A= abc
=relationship between absorption of light by a solution and concentration of that solution
-A is directly proportional to concentration and distance light travels through a solution (b) which is consistent
A = absorbance
a = molar absorptivity (constant for solution of any concentration if measured at a specific wavelength). light absorbing ability of a substance under specific conditions. absorbance per unit concentration and unit path length
b=light path length through solution (cm)
c = concentration [M] in mol/L
what is molar absorptivity
a is absorptivity when concentration is 1 mol/L [M] and light path is 1 cm = M^-1 cm ^-1
a is the characteristic of a substance and can be used to check purity and calculate concentration
