Flashcards in Electromagnetic radiation L3 Deck (37)
Loading flashcards...
1
what forms EMR
made by motion of electrically charged particles
2
what does EMR do
emits from these particles as periodic oscillations of electric and magnetic fields through time and space (‘waves’)
3
why is EMR described as having a dual personality
Besides acting like waves, it also acts like a stream of particles (called "photons") that have no mass
4
what makes EMR wave-like
behaves as a stream of particles ‘photons’ that transfer energy but have no mass
5
where does EMR travel through
empty space (vacuum) as well as through air and other substances
6
what is the structure of EMR like
electric and magnetic fields are orthogonal (at right angles) to one another
7
what are frequency and wavelength related to in a wave
velocity (speed) of the wave thus:
c = fλ
c is the speed of light (3x108 m.s-1);
f is the frequency (Hz)
λ is the wavelength (m)
8
what happens to wavelength if frequency increased
lower
9
what happens to frequency if wavelength increased
lower
10
what does E=hf mean
energy contained in an individual quantum (photon) of electro-magnetic radiation depends upon its frequency
11
how does EMR effect quantum energy
Higher the frequency of the EMR the higher its quantum energy
12
which part of EMR is highest energy
gamma rays, x-rays
13
which part of EMR is lowest energy
radio waves
14
how does quantum energy change
Quantum energy increases with increasing frequency (reducing wavelength)
15
what does quantum energy determine
biological/chemical effects
16
which has a higher quantum energy
-chemically active EMR
-thermal radiation
chemically active EMR
17
which part of EMR significantly damages cells
gamma rays
x-rays
18
what effect does UV and short visible EMR wavelength have
has enough energy to cause chemical transformations
e.g.photosynthesis
19
what effect does IR, longer wavelength visible EMR and short microwaves have
sufficiently energetic for significant transfer of heat
20
what effect do radio waves have
transfer very small amounts of energy
21
what is the most important EMR source
solar spectrum
22
what is the solar spectrum wavelengths
mainly UV, visible and IR
23
what is PAR
photosynthetically active radiation
24
does photosynthetically active radiation effect chemical bonds
EMR which has appropriate quantum energy to change chemical bonds – specifically in photosynthesis
25
what wavelength is photosynthetically active radiation
UV-visible wavebands
26
how much EMR from the sun is PAR
not all of the EMR received from sun is photosynthetically active (approx. 50% of solar radiation is PAR)
27
what effect does thermal radiation have
EMR, has effect of transferring energy (heat) but not any other effects (e.g. chemical changes)
28
how does thermal radiation effect chemical bonds
no direct chemical effects as quantum energy is too low to disturb chemical bonds
29
when is thermal radiation emitted
All ‘hot’ surfaces emit spectrum of thermal radiation (hot is anything > absolute zero)
30
