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Refraction and Reflectance: Understanding the Interaction of Light with Different Media, Slides of Analytical Chemistry

Lakshmibai National Institute of Physical Education Analytical Chemistry

An in-depth analysis of the reflection and refraction of electromagnetic waves at the boundary between two media with different refractive indices. Topics covered include specular reflection, reflectance, critical angle, polarization, and absorption and emission. The document also discusses the importance of these concepts in various fields such as refractometers and fiber optics.

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Reflection = EM strikes a boundary between

two media differing in ηand bounces back

Specular reflection = situation where angle of

incidence (θi) equals angle of reflection (θr)

Medium 1 (air)

η= 1.00

Medium 2 (glass)

η= 1.50

Incident

ray

θ1θ2

Reflected

ray

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Reflection

= EM strikes a boundary between

two media differing in

and bounces back

Specular reflection = situation where angle of

incidence (

i) equals angle of reflection (

Medium

(air)

1 .

Medium 2 (glass)

1 .

rayIncident

θ 1

θ 2

ray Reflected

I r ( η 2 - η 1 ) 2

Reflectance = R =

I i ( η 2 + η 1 ) 2

Where I

and I

= incident & reflected intensity

For radiation going from air (

.00) to glass

.50) as shown in previous slide

R = 0.04 = 4 %

Many surfaces at 4 % each (i.e., many lenses) can

generatescause serious light losses in a spectrometer. This

stray radiation

or

stray light

EM going from glass (

1 .50) to air (

1 .00)

Percent Reflectance (R)

Angle of Incidence (

θ i)

η medium of higherEM going from a

to a medium of

lower

η , the angle

reflected backlight is completelybefore all of thethe critical angleonly increase toof incidence can

R = 4 %

AngleCritical

Critical Angle

Ф

to surface Normal

Medium

(air)

Medium 2 (glass)

90 ray isIncident

o to

grazing incidencethis is callednormal

Ф

ray Refracted

Maximum value of

Ф

2 (^) =

Ф

At 90

incidence sin

Ф

sin

Ф

1 Important for: ) Refractometers

Fiber Optics

Critical Angle

Ф

to surface Normal

MediumMedium 2 (air)

(glass)

Ф

rayIncident

New value of

Ф

1 (^) for

Reflection

Ф

> (^) Ф

Critical angle, At angles greater than the

Total Internal Reflectance reflection occurs or

1 Important for: ) Refractometers

Fiber Optics

rayRefracted

rayReflected

EM is said to be unpolarized if its electric Polarization

equal amplitude in all directionvectors and magnetic vectors occur with

Linearly polarized light oscillates in one

plane only as it moves through space

at 90polarized and H vector is Here E vector is vertically

in horizontal plane

Circularly polarized light rotates in either a

moves through spaceleft handed or right handed spiral as it

follows, but is offset by 90polarized and H vectorHere E vector is circularly

docsity.co

Two most interesting and most useful Absorption and Emission

processes when EM interacts with matter

Atoms and molecules can exist in many

possible energy states

Consider two states

E

Absorption

Emission

State

Ground StateExcited StateState 2

∆ For absorption of EM

E = E

= h

Where E

1 & E

2 are

ν h is Planck’s constantenergies of states &

is the frequency

Have to consider particle nature of EM for

of photons with energy habsorption – consider EM to be a bundle

The rate of absorption or emission depends

on:

stateNumber of atoms/molecules in initial

particular transitionProbability that is characteristic of the

Radiation density

Stimulated Emission - photon strikes

state 2 causing it to emit

dN

------ = N

2 B 2 1 ρ ( ν )

dt

Relationship between probability coefficients

B

1 2

= B

2 1

Absorption

Stimulated Emission

A

2 1

h

B^

1 2

Boltzmann Distribution – relative population

of states

& 2 is dependent on energy

difference and temperature at equilibrium

N

e

-E

1 /kT

N

e

-E

2 /kT

K = Boltzmann’s constant

(8.62 x

eV/

o K)

T = absolute temperature

o K = 25

o C)

An additional term is add to the right side of

state with the same energy = degeneracythe equation if there is more than one

R O Y

G

B V

SpectroscopyRayGamma

FluorescenceAbsorption,X-Ray

FluorescenceAbsorption,UV-vis

SpectroscopyAbsorptionInfrared

SpectroscopyAbsorptionMicrowave

EPRNMR

Transitions Nuclear

ElectronsInner Shell

ElectronsOuter Shell

VibrationsMolecular

RotationsMolecular

StatesSpin

Quantitative Aspects of Absoption

Beer-Lambert Law (or Beer’s Law)

I

A = log ---- =

b C

I

T = ----

%T = T x

I

= measured source intensity

Intensity change does not change absorbanceI = measured intensity after absorptionAbsorbance

Transmittance

molar absorptivity

concentration

path length

Refraction and Reflectance: Understanding the Interaction of Light with Different Media, Slides of Analytical Chemistry

Related documents

Partial preview of the text

Download Refraction and Reflectance: Understanding the Interaction of Light with Different Media and more Slides Analytical Chemistry in PDF only on Docsity!

Reflection

= EM strikes a boundary between

two media differing in

and bounces back

Specular reflection = situation where angle of

incidence (

i) equals angle of reflection (

I r ( η 2 - η 1 ) 2

Reflectance = R =

I i ( η 2 + η 1 ) 2

Where I

and I

= incident & reflected intensity

For radiation going from air (

.00) to glass

.50) as shown in previous slide

R = 0.04 = 4 %

Many surfaces at 4 % each (i.e., many lenses) can

generatescause serious light losses in a spectrometer. This

stray radiation

or

stray light

R = 4 %

Critical Angle

Ф

Ф

Ф

Ф

Ф

At 90

incidence sin

Ф

sin

Ф

Critical Angle

Ф

Ф

Ф

Ф

Critical angle, At angles greater than the

Total Internal Reflectance reflection occurs or

EM is said to be unpolarized if its electric Polarization

equal amplitude in all directionvectors and magnetic vectors occur with

Linearly polarized light oscillates in one

plane only as it moves through space

Circularly polarized light rotates in either a

moves through spaceleft handed or right handed spiral as it

Two most interesting and most useful Absorption and Emission

processes when EM interacts with matter

Atoms and molecules can exist in many

possible energy states

Consider two states

E

∆ For absorption of EM

E = E

= h

Have to consider particle nature of EM for

of photons with energy habsorption – consider EM to be a bundle

The rate of absorption or emission depends

on:

stateNumber of atoms/molecules in initial

particular transitionProbability that is characteristic of the

Radiation density

Stimulated Emission - photon strikes

state 2 causing it to emit

dN

------ = N

2 B 2 1 ρ ( ν )

dt

Relationship between probability coefficients

B

= B

Absorption

Stimulated Emission

A

h