9848 Lecture Notes - Lecture 8: Longitudinal Wave, Photon, Radiation Therapy
19 Jun 2018
School
Department
Course
Professor
Intro to Radiation Safety Continued
Radiation
is a transfer of energy
•some examples= sound , electromagnetic (more on this soon) , radiant heat , particles
eg beta (β) particles eg. β- or β+ , ejected electrons (e-) during ionisation , alpha (α)
particles
Waves
a wave is something that varies cyclically (reacurrant)
• 2 types, longitudinal and transverse
eg sound is longitudinal wave in a rope is transverse ◦ ◦
• in cross-section both can be seen to have a sine pattern
Describing waves – 6 ways
1. wavelength (λ the Greek symbol lambda) – unit in m
2. amplitude (A) – unit in m
3. wave velocity (v) – unit in m s-1 (v = f λ) -
NB. for EM radiation v = C (the speed of
light)
4. frequency (f or the Greek symbol nu) –
unit in Hz (s-1) (f = v / λ)
5. period (T) – unit in s (T = 1 / f) is the time
between waves at a given point
6. phase – measured in angle (degrees or
radians)
Electromagnetic Rdiation
•EM radiation is a form of
energy
•it has characteristics of both
waves and particles
• in its wave form it has both
electric and magnetic field
components. These are perpendicular to each other and perpendicular to the direction
of the wave
•the electric and magnetic field support each other allowing the waves to travel through
vacuums
find more resources at oneclass.com
find more resources at oneclass.com
- all other waves such a sound or waves in water need a medium (air or the water) to
support the wave
•as per all waves, each type of EM radiation has a:
wavelength (λ) ◦
frequency (ν) ◦
and travels at a velocity. The velocity is the speed of light (C) ◦
Wave Nature of EM Radiation
•all EM radiation travels at the speed of light (C) which is approximately 3 x 108 ms-1 (or
nearly 8 times around the Earth’s equator in a second)
• wavelength λ (m) given by
where C = speed of light (m s-1) ν = frequency (Hertz or s-1) ◦
•also can think of:
•it can be seen from the above equation that if ↑λ there will be a
proportionally ↓ν as C is a constant
-ie λ and ν are inversely proportional
Frequency and wavelength explained
•wavelength is the distance between one point on one wave and the same point on the
next wave
λ of light range from 400 nm (400 x 10-9 m) to 700 nm◦
λ of radio waves are in the order of 100’s of metre◦
λ of x-ray are typically 1 x 10-10 to 1 x 10-11 m ◦
•frequency is how often the same point in consecutive waves that pass a point in a
second
ν of light is aprox 1 x 1015 Hertz (or s-1) ◦
ν of radio waves is aprox 1 x 107 Hertz (or s-1)◦
ν of x-ray is aprox 1 x 1019 Hertz (or s-1)◦
EM Radiation Chart
find more resources at oneclass.com
find more resources at oneclass.com
Particle Nature of EM Radiation
•in its particle form it can be described as discreet bundles of energy
• a photon is the smallest discreet bundle of energy of EM radiation
this is also called a quantum ◦
•photons have no mass, no electrical charge and can be considered as particles
travelling at the speed of light
•the approximate number of light photons emitted from a light globe is in the order of
3 x 10 ^19 per second
EM Radiation
•examples of EM radiation are radio waves (RF), radar, visible light, infrared and UV light,
microwaves, x-rays, γ rays.
• other things in common:
all travel at the speed of light, C, 3.0 x 10^8 m s-1 ◦
can be thought of as either waves or particles (photons) of energy; Wave – Particle ◦
Duality
travels in straight lines (through a vacuum) emanating (spread out ) from a point (ie ◦
radiates)
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Radiation is a transfer of energy some examples= sound , electromagnetic (more on this soon) , radiant heat , particles eg beta ( ) particles eg. - or + , ejected electrons (e-) during ionisation , alpha ( ) particles. Waves a wave is something that varies cyclically (reacurrant: 2 types, longitudinal and transverse eg sound is longitudinal wave in a rope is transverse, in cross-section both can be seen to have a sine pattern. Describing waves 6 ways: wavelength ( the greek symbol lambda) unit in m. 3. wave velocity (v) unit in m s-1 (v = f ) - Nb. for em radiation v = c (the speed of light) 4. frequency (f or the greek symbol nu) unit in hz (s-1) (f = v / ) 5. period (t) unit in s (t = 1 / f) is the time between waves at a given point. 6. phase measured in angle (degrees or radians)
