The Origin of EM Radiation

Question 1

What is flux?

Answer 1

flow (per unit time); often qualified with an appropriate quantity

Question 2

What is fluence?

Answer 2

‘concentration’ (per unit area); often qualified with

an appropriate quantity

Question 3

What is energy flux (W) or power?

Answer 3

energy per unit time

Question 4

What is flux density?

Answer 4

(particles/m2)

The number of photons striking unit (normal) area in unit time.

Question 5

What is intensity?

Answer 5

(W/m2)

The energy incident per unit (normal) area per unit time

Question 6

What is radiant energy?

Answer 6

(J)

The energy radiated by a source

Question 7

When is 1 Joule of work done?

Answer 7

when a Coulomb moves across a potential of 1V

Question 8

When is 1 eV of work done?

Answer 8

when a single electron moves across a potential of 1V

Question 9

What is electrostatics?

Answer 9

Like charges repel

Unlike charges attract

Question 10

What is the concept of potential?

Answer 10

Work is done when a force causes movement (dW = F. d x)‏

Question 11

What does electromagnetic radiation look like?

Answer 11

Electromagnetic disturbance propagating through space.

Time varying electric (E) and magnetic (B) fields. The electric component does most of the interacting with matter.

Question 12

What is the speed of EM radiation?

Answer 12

Speed (c)
3x108ms-1 in a vacuum
1 foot in 1ns
1,000,000 miles in 5secs

Question 13

What is the frequency of EM radiation?

Answer 13

Frequency (v)
Oscillations per
second (Hz)

Question 14

What is the wavelength of EM radiation?

Answer 14

Wavelength (y)
Peak-to-peak distance
of wave (metres)

Question 15

What is the duality of EM radiation?

Answer 15

EM radiation can be considered to be both particulate and wave-like in nature.

Question 16

What is the polarisation of EM radiation?

Answer 16

Polarisation refers to the imposing of a well defined plane of oscillation on the electric vectors of electro-magnetic waves.

Question 17

What is the intensity of EM radiation?

Answer 17

A measure (energy) of the number of photons striking unit area in unit time.

Question 18

What is the coherence of EM radiation?

Answer 18

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.

Question 19

What is the absorption of EM radiation?

Answer 19

The transfer of a photon’s energy to surrounding material.

Question 20

What is the scatter of EM radiation?

Answer 20

The random re-direction of a photon’s path.

Question 21

What is the attenuation of EM radiation?

Answer 21

The decreasing photon flux resulting from interaction processes as light travels through a medium. (Beers Law; I=I0e-ux)

Question 22

What is the relflection of EM radiation?

Answer 22

The ordered redirection of EM radiation that occurs when it ‘bounces’ off a smooth surface.

Question 23

What is the refraction of EM radiation?

Answer 23

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)

Question 24

What is the diffraction of EM radiation?

Answer 24

The spreading of light that occurs as it passes an edge.

Question 25

What are implications of EM radiation

Answer 25

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)

Question 26

What is a proton?

Answer 26

propagating discontinuity (speed ‘c’) in the equilibrium electric field

Question 27

What does an accelerating charge produce?

Answer 27

such a discontinuity (ie.it radiates)

Question 28

What is the energy radiated wave related to?

Answer 28

acceleration of the charge

Question 29

What are the interaction of EM radiation?

Answer 29

absorption
scatter
attenuation
reflection
refraction
diffraction