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Flashcards in Electromagnetic radiation L3 Deck (37)
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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

what effects the wavelength of thermal radiation

Wavelength of peak emission and rate of emission depend on temperature of the surface