Electromagnetic Spectrum – Properties - Instrumental Methods of Analysis B. Pharma 7th Semester

Electromagnetic Spectrum – Properties

Session Objectives

By the end of this session, students will be able to:

Ø  Explain the properties of Electro Magnetic waves

Ø  Correlate different components of Electro Magnetic spectrum with different Spectroscopic methods

Properties of EM Waves

       All matter contains charged particles that are always moving; therefore, all objects emit EM waves.

       The wavelengths become shorter as the temperature of the material increases.

       EM waves carry radiant energy. 

What is the speed of EM waves?

       All EM waves travel 300,000 km/sec in space. (speed of light-nature’s limit!)

       EM waves usually travel slowest in solids and fastest in gases.

Material

Speed (km/s)

Vacuum

300,000

Air

<300,000

Water

226,000

Glass

200,000

Diamond

124,000

What is the wavelength & frequency of an EM wave?

       Wavelength= distance from crest to crest.

       Frequency= number of wavelengths that pass a given point in 1 s.

       As frequency increases, wavelength becomes….

       Wavelength (λ)= distance between consecutive crests or troughs.

     Units: meters (m)

       Frequency (ѵ) = number of wavelengths that pass a given point in 1 s. The SI unit of frequency is the hertz (Hz)/ cycles per second (cps)

       As frequency increases, wavelength becomes smaller.

       Wave number (ṽ) is the number of waves per unit distance 

       m-1                                             ν=C/λ=CV

Can a wave be a particle?

       In 1887, Heinrich Hertz discovered that shining light on a metal caused electrons to be ejected.

       Whether or not electrons were ejected depended upon frequency not the amplitude of the light!  Remember energy depends on amplitude.

       Years later, Albert Einstein explained Hertz’s discovery:  EM waves can behave as a particle called a photon whose energy depends on the frequency of the waves.

       Electrons fired at two slits actually form an interference pattern similar to patterns made by waves


What did Young’s experiment show?

Electromagnetic Waves

How they are formed

Waves made by vibrating electric charges that can travel through space where there is no matter

Kind of wave

Transverse with alternating electric and magnetic fields

Sometimes behave as

Waves or as Particles (photons)

EMR and Spectroscopy

Technique

Type of Electromagnetic Radiation

Type of Matter Observed

Type of Interaction

Ultraviolet-Visible Spectroscopy
(UV-Vis Spectroscopy)

Ultraviolet and Visible radiation

Electrons and electronic excitations

Absorbance

Infrared Spectroscopy
(IR Spectroscopy)

Infrared radiation

Molecular rotations, molecular vibrations, bonds between atoms

Absorbance (or transmittance)

Fluorescence Spectroscopy

Ultraviolet and Visible radiation

Electrons and electronic excitations

Emission

Nuclear Magnetic Resonance Spectroscopy (NMR Spectroscopy)

Radiowaves

Nucleus

Resonance or Coherance

Flame emission spectroscopy (Flame photometry)

Ultraviolet and Visible radiation

Atoms

Emission

X-Ray Diffraction Crystallography

X-rays

Electron denisities

Diffraction or Scattering

Atomic Absorption and Emission Spectroscopy

Ultraviolet and Visible radiation

Atoms

Absorption or Emission

ESR Spectroscopy

Microwaves

Free radicals

Absorption

Certain terms used in spectroscopy

       Spectroscopy

       Spectrophotometry

       Spectrometer: an instrument with an entrance slit, a dispersing device, and one or more exit slits, with which measurements are made at selected wavelengths within the spectral range, or by scanning over the range. The quantity detected is a function of radiant power

       Photometer an instrument used in photometry, usually one that compares the illumination produced by a particular light source with that produced by a standard source 

       Spectrophotometer: A spectrophotometer is a combination of two instruments, namely a spectrometer for producing light of any selected color (wavelength), and a photometer for measuring the intensity of light.

SUMMARY

       Wavelength= distance from crest to crest.

       Frequency= number of wavelengths that pass a given point in 1 s.

       Wave number (ṽ) is the number of waves per unit distance 

       m-1                                            

      ν=C/λ=CV

 For PDF Notes Click on Download Button   

Post a Comment

0 Comments