Electromagnetic Radiation
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What is electromagnetic radiation composed of?
Oscillating electric and magnetic fields.
What is electromagnetic radiation?
A form of energy that can interact with atoms and molecules
What does all electromagnetic radiation travel in?
Waves at the speed of light
What is the speed of light( number)?
3x10’8 ms-1
What is a wave defined by?
It’s wavelength and it’s frequency
What is wave length?
Distance between adjacent crests
What is frequency?
Number of waves that pass a fixed point in one second
What is the wave number?
Number of waves per metre
What is the relationship between frequency and wavelength ?
Frequency is inversely proportional to wavelength Short wave length= high frequency Long wavelength = low frequency
What are photochemical reactions initiated by?
Electromagnetic radiation from the visible and ultraviolet region of the spectrum
What is the unit of wavelength?
Nanometre
What is the visible region of the spectrum?
400-700nm Blue. Red
What is the ultraviolet range?
~200-400nm
What does electromagnetic radiation behave as ?
A stream of particles which carry energy - these particles are called photons
What can photons do?
Interact with electrons in atoms
What happens when atoms absorb photons?
Electrons in the atom gain energy and are now in an excited state
What happens when atoms emit photons?
They lose energy and return to ground state
What is equation given for the energy of a photon?
E=hf
What is planks constant?
6.63x10-34
What is the equation given for the energy of one mole of photons ?
E= hf x avodgadro’s constant
What is the equation for the relationship between wavelength, frequency and velocity ?
C= lambda x frequency
What are many reactions involving halogens initiated by?
Light
Describe initiation?
Production of the first free radical (always halogen)
Describe propagation ?
Maintains the supply of free radicals