Electromagnetic Radiation Flashcards
On the electromagnetic spectrum describe which direction it increases in frequency and which direction increases in wavelength
from right to left has increasing frequency (Hz)
from left to right has increasing wavelengths (lamda)
Describe properties of all types of electromagnetic radiation - 7 points
carry energy, travel at 3 x 10 to the power 8 ms to the -1 (speed of light ‘c’), can travel in a vacuum (sound needs a vacuum), their intensity obeys the Inverse Square Law, unaffected by electric and magnetic fields, travel in straight lines, have frequency, wavelength and amplitude
Describe ionising radiations
some types of wave (e.g. x-ray/gamma rays) can ionise atoms, can be harmful
Describe non-ionising radiations
other types of wave (e.g. infra-red and radio) cannot ionise matter
Name the 2 models of electromagnetic radiation
The wave model, the proton model
The electromagnetic wave is composed of …
sinusoidally alternating electric and magnetic fields
Define wavelength (lambda)
the distance between corresponding points on 2 consecutive cycles
Define frequency (f)
number of complete cycles occurring p/s - Hz
Define period (T)
time taken for the wave to complete 1 cycle, T = 1/f
V = f(lambda)
Velocity = frequency x wavelength
Define amplitude
the “vigour” of the wave
Define cycle
One complete oscillation of the wave
Quanta/Photons
a more appropriate term for electromagnetic radiation, a stream of discrete ‘packets’ of energy
Equation for the amount of energy photons have carried
E = h x f, E = photon energy (J), h = Planck’s constant (6.626 x 10 to the power of -34 J.S), f = frequency of radiation (Hz)
a substitute for f = c/(lambda)
‘Wave particle duality’
the wave theory and the photon theory existing simultaneously - each can be used to explain different phenomena (interference - best explained using wave theory, x-ray production/absorption - best explained using photon theory)
Define spectrum
a spectrum is a graph which shows the energy distribution of the radiation present, whatever its type
Define Intensity
amount of energy flowing per unit area, per unit time, measured along a plane at 90 degrees to the direction of travel of the radiation
J.m^-2.s^-1 Joules per metre squared per second
Describe the inverse square law
intensity of radiation from a point source varies inversely with the square of the distance from the source provided there’s no attenuation by the medium through which the beam is travelling
Intensity is proportional to 1 over the distance squared
I a 1/d squared
As the distance from the source of radiation gets greater, the intensity of that radiation …
get smaller
The inverse square law is significant in practice when …
calculating exposure factors, radiation protection requirements, radiation dose
I1 x (d1) squared = I2 x (d2) sqaured ^^ write this out in words
Intensity at the original distance times the original distance squared equals the intensity at the new distance times the new distance squared
X-Rays are measured in
keV
Define stochastic
random (cancer odds)
Define deterministic
known threshold (hairloss)
Define somatic
happens to patients through radiation
Define genetic
passes onto offspring - radiated parent
Which 4 places do X-Rays originate from
outer space/radioisotopes/X-Ray tubes/linear accelerators
