Exam 1

Question 1

What is the wave model of light?

Answer 1

Electromagnetic waves propagate with an electric field perpendicular to the magnetic field where both oscillate perpendicular to the direction of propagation

Question 2

What is the equation for frequency?

Answer 2

1/T

Question 3

What is the equation for speed of light in terms of wavelength and frequency?

Answer 3

lambda*mu = c

Question 4

the frequency of the light is invariant and is dependent on the source

Answer 4

wave model of light

Question 5

the speed of light depends on the medium through which is travels

Answer 5

wave model of light

Question 6

what is the index of refraction?

Answer 6

The index of refraction of the medium is the ratio of the speed of light in vacuum to the speed of light in the medium

Question 7

orientation of the electric field determines the polarization of the electromagnetic wave

Answer 7

linear polarization/plane polarization

Question 8

only allows one plane of polarization to pass through

Answer 8

polarizer

Question 9

What is the double-slit experiment?

Answer 9

When light passes through two closely spaced slits, an interference pattern is produced.

Question 10

a result of adding waves that are in phase

Answer 10

constructive interference

Question 11

a result of adding waves that are out of phase

Answer 11

destructive waves

Question 12

how do you describe the interaction of matter with light?

Answer 12

interaction of irradiation with matter. refer to the light as photons

Question 13

what is the energy of one quanta of light?

Answer 13

E=hv

Question 14

molecules may exist in discrete energy states called…

Answer 14

steady states

Question 15

do atoms have vibrational and rotational energy?

Answer 15

no, only molecules

Question 16

lowest energy state

Answer 16

ground state

Question 17

__________ produced in the UV and visible region of the spectrum when the radiating species are individual atomic particles that are well separated in the gas phase

Answer 17

line spectra

Question 18

_____ determines the distribution of molecules populating an excited state over a ground state

Answer 18

boltzmann distribution

Question 19

as the fraction of molecules populating the excited state increases…

Answer 19

absorbance intensity decreases

Question 20

the frequencies absorbed by atoms and molecules are characteristic of…

Answer 20

the molecule and its interaction with the solvent

Question 21

The many discrete peaks in the
absorption spectrum come from excitation from the ground vibrational state to excited vibrational states in the excited electronic state.

Answer 21

vibrational fine structure

Question 22

uncertainty principle: the shorter the lifetime…

Answer 22

the broader the band. things that shorten the lifetime include collisions with solvent or solute

Question 23

how is transmittance defined?

Answer 23

power incident divided by transmitted power

Question 24

how is absorbance defined?

Answer 24

-logT

Question 25

Beer-Lambert law

Answer 25

absorbance is proportional to the thickness of the sample, the concentration and a property inherent to the sample, the molar absorptivity

Question 26

how close our instrument comes to measuring a "true value"

Answer 26

accuracy

Question 27

how do you calibrate an instrument?

Answer 27

take the mean of several measurements

Question 28

For addition and subtraction the final error is just the square root of the sum of errors squared, while for multiplication and division the relative error of the final calculation is the square root of the sum of relative errors squared. The relative error is just the error divided by the mean.

Answer 28

propagation of error

Question 29

What is a null hypothesis

Answer 29

there is no difference between the two samples

Question 30

determines if the standard deviations of the two distributions differ significantly from one another

Answer 30

F test

Question 31

determines if the means of samples are different

Answer 31

t test (two means), ANOVA (multiple means)

Question 32

what are the typical spectroscopic instrument components?

Answer 32

1. Source lamp/heated solid 2. sample holder 3. wavelength selector 4.photoelectric transducer 5. signal processor and readout

Question 33

______ emits radiation over a broad range of wavelengths, with a relatively smooth variation in intensity

Answer 33

continuum source

Question 34

_______ emits radiation at discrete wavelengths, with broad regions showing no emission lines

Answer 34

line source

Question 35

What are examples of continuum sources?

Answer 35

Deuterium lamp - UV range tungsten lamps - UV to Near IR argon lamp - VAC nernst glower - UV- Far IR nichrome wire - Near IR - far IR globar Near IR- Far IR

Question 36

What are examples of line sources?

Answer 36

hollow cathode lamps - UV - Visible lasers - VAC - IR

Question 37

what does a narrow bandwidth do for measurements?

Answer 37

enhances sensitivity of absorbance and provides selectivity for absorption and emission spectra

Question 38

narrow continuous group of wavelengths

Answer 38

band

Question 39

the width of a band at half-height

Answer 39

effective bandwitdth

Question 40

what are the two basic ways to select wavelengths?

Answer 40

Filters and Monochromators

Question 41

What are the components of a monochromator?

Answer 41

1. Entrance slit 2. Collimating lens or mirror 3. prism or grating 4. focusing element 5. exit slit

Question 42

what does a collimating lens do to the light?

Answer 42

makes it parallel

Question 43

why are monochromators better than prisms?

Answer 43

Nearly all commercial monochromators are based on gratings because they are cheaper to make, provide better wavelength separation for the same size element and disperse radiation linearly on the focal plane

Question 44

what are examples of continuum wavelength selectors?

Answer 44

fluorite prism - VAC fused silica or quartz - UV to near IR glass prism - Visible - Near IR NaCl - Near IR - far IR KBr prism - IR - Far IR

Question 45

what are examples of discontinuous wavelength selectors?

Answer 45

interference wedge - visible to far IR interference filter - UV to Far IR glass filters - visible to near IR

Question 46

____ is the variation in wavelength along the line AB in the focal plane

Answer 46

the reciprocal of linear dispersion (nm/mm)

Question 47

_______ is the ability to separate two wavelengths of bandwidth delta lamba

Answer 47

resolving power (smaller distances between gratings increase resolving power)

Question 48

what do most modern monochromators use?

Answer 48

echelle grating