Electromagnetic spectrum - PowerPoint PPT Presentation

1 / 10
About This Presentation
Title:

Electromagnetic spectrum

Description:

Electromagnetic spectrum & visible portion Violet (400 nm) Red (700 nm) White = ROYGBV (can be separated by dispersion) Electromagnetic waves (visible light, X-rays ... – PowerPoint PPT presentation

Number of Views:125
Avg rating:3.0/5.0
Slides: 11
Provided by: skissin
Category:

less

Transcript and Presenter's Notes

Title: Electromagnetic spectrum


1
  • Electromagnetic spectrum visible portion
  • Violet (400 nm) ? Red (700 nm)
  • White ROYGBV
  • (can be separated by dispersion)

2
Electromagnetic waves (visible light, X-rays,
etc.)
  • Wave Theory
  • Wavelength l Distance between peaks
  • Frequency no. of waves/sec to pass a given
    point (hertz)
  • frequency v/l , v velocity

f
3
Pertinent Units
  • Wavelength nm (mµ) 10-9m
  • old units, Å 10-8m
  • Frequency hz (cycles/sec)
  • Energy units (at the atomic scale) are also
    sometimes used. Energy in eV ??, where ? is
    Planck,s constant. 1Å is equivalent to
    1.24x10-24eV.

4
Polarization
  • Non-polarized (usual) light
  • Each photon vibrates as a wave form in a single
    plane. Vibration refers to the rise and fall of
    the sine wave.
  • Light beam is composed of numerous photons, each
    vibrating in a different plane.
  • Vibration occurs in all directions
    perpendicular to propagation direction

5
Polarization
Plane of interface surface of crystal Plane of
incidence T-N-U-V-M-S-O Plane of
incidence contains incident, reflected and
refracted ray paths as well angles i, l and r
6
  • Refraction
  • Incident ray and reflected ray
  • 1) ? of incidence i ? of reflection r
  • 2) coplanar in the plane of incidence
  • Refracted ray
  • 1) Slower in water or glass
  • 2) ?r (refraction) ? ? i (incidence)
  • Depends on D v

Incident
Reflected
i
r
air
water
r
Refracted
7
Index of refraction
  • For a substance x
  • nx vvacuum/vx
  • nair 1.0003
  • light is slower in water, glass, crystals
  • Is nwater greater or less than 1?
  • Larger n associated with slower v !
  • Snells Law (1621)
  • ni sin i nr sin r
  • for two known media (air/water),
  • sin i/sin r nr / ni const.
  • So can predict angle change (or use it to
    determine nr)

8
Polarization
incoming ray is non-polarized
reflected and refracted rays both become polarized
  • Note symbolization used
  • Reflected ray polarized perpendicular to the
    plane of incidence.
  • Refracted ray polarized in plane of incidence.

9
Interference
Fig 7-1 Bloss, Optical Crystallography, MSA
  • A Particles in phase if displaced from rest
    position by same amount in same direction
  • a1 - a2 - a3 are all in phase
  • b1 - b2 - b3 are also all in phase (but not with
    a1)
  • particles perfectly out of phase
    equal-but-opposite displacement
  • b1 and c1 are not perfectly out of phase

10
Interference
Fig 7-1 Bloss, Optical Crystallography, MSA
  • path difference (D) distance between any 2
    points on a wave form
  • usually expressed as xl
  • D between any 2 points in phase il (iany
    integer)
  • D between any 2 points perfectly out of phase
    ((2i1)/2) l/2
Write a Comment
User Comments (0)
About PowerShow.com