The Origin of EM Radiation Flashcards
What is flux?
flow (per unit time); often qualified with an appropriate quantity
What is fluence?
‘concentration’ (per unit area); often qualified with
an appropriate quantity
What is energy flux (W) or power?
energy per unit time
What is flux density?
(particles/m2)
The number of photons striking unit (normal) area in unit time.
What is intensity?
(W/m2)
The energy incident per unit (normal) area per unit time
What is radiant energy?
(J)
The energy radiated by a source
When is 1 Joule of work done?
when a Coulomb moves across a potential of 1V
When is 1 eV of work done?
when a single electron moves across a potential of 1V
What is electrostatics?
Like charges repel
Unlike charges attract
What is the concept of potential?
Work is done when a force causes movement (dW = F. d x)
What does electromagnetic radiation look like?
Electromagnetic disturbance propagating through space.
Time varying electric (E) and magnetic (B) fields. The electric component does most of the interacting with matter.
What is the speed of EM radiation?
Speed (c)
3x108ms-1 in a vacuum
1 foot in 1ns
1,000,000 miles in 5secs
What is the frequency of EM radiation?
Frequency (v)
Oscillations per
second (Hz)
What is the wavelength of EM radiation?
Wavelength (y)
Peak-to-peak distance
of wave (metres)
What is the duality of EM radiation?
EM radiation can be considered to be both particulate and wave-like in nature.
What is the polarisation of EM radiation?
Polarisation refers to the imposing of a well defined plane of oscillation on the electric vectors of electro-magnetic waves.
What is the intensity of EM radiation?
A measure (energy) of the number of photons striking unit area in unit time.
What is the coherence of EM radiation?
This is the extent to which one part of the E-M field can be described, knowing its state at a different point in time or space.
What is the absorption of EM radiation?
The transfer of a photon’s energy to surrounding material.
What is the scatter of EM radiation?
The random re-direction of a photon’s path.
What is the attenuation of EM radiation?
The decreasing photon flux resulting from interaction processes as light travels through a medium. (Beers Law; I=I0e-ux)
What is the relflection of EM radiation?
The ordered redirection of EM radiation that occurs when it ‘bounces’ off a smooth surface.
What is the refraction of EM radiation?
The bending of radiation as it crosses a refractive index boundary. (Snell’s law and light; n1sin(theta)1=n2sin(theta)2, n=c/v)
What is the diffraction of EM radiation?
The spreading of light that occurs as it passes an edge.
What are implications of EM radiation
Accelerating charge is the mechanism responsible for the production of EM waves
- Radio waves (charges accelerated along an aerial)
- Microwave (charges accelerated in a magnetron/klystron)
- Light (charges accelerated between energy levels in atoms)
- X-rays (charges decelerated on striking a target anode)
What is a proton?
propagating discontinuity (speed ‘c’) in the equilibrium electric field
What does an accelerating charge produce?
such a discontinuity (ie.it radiates)
What is the energy radiated wave related to?
acceleration of the charge
What are the interaction of EM radiation?
absorption scatter attenuation reflection refraction diffraction
