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Lecture 3 Describe Newtons ‘experimentum crucis’ and how it fundamentally changed our understanding of colour and light. Define wavelength and frequency. Name all parts of the electromagnetic spectrum.

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Natural Science
NATS 1870
Robin Kingsburgh

SC NATS 1870 (lecture) Monday, September 28, 2009 Describe Newtons ‘experimentum crucis’ and how it fundamentally changed our understanding of colour and light.  Prism  red light  prism = red light  Color is an intrinsic property of light Define wavelength and frequency.  Wavelength  peak to peak distance  Frequency  how many waves pass in a second Name all parts of the electromagnetic spectrum.  Gamma, x-ray, ultraviolet, visible, infrared & radio  High energy  --------------------------------  low energy  Human eye can see Sketch a spectrum for (i) a red light and (ii) a red piece of paper. Label the axes. Red Light Red Paper I I The amount of The amount of light emitted per light emitted per wavelength wavelength 400 500 600 nm 400 500 600 nm B G R hue B G R hue  Reflective speed  Light travels @ the speed of light  Height is more of value  Color results from interaction between light & matter WHITE LIGHT RED Eye/brain perceives Red object (Mixture of all colors) falls upon red surface  Only red wavelengths are reflected into our eye  All other wavelengths have been absorbed by red surface, WHY?  Molecules/atoms on red surface selectively absorb certain wavelength of light, leaving only red wavelengths to be reflected  Atoms made of protons, neutrons, electrons  Protons = p  positively charged  Neutron = neutral  Electrons = e-  negatively charged  Nucleus: p & n orbited by e-  The # of protons dictates the type of atom  Simplest: hydrogen -1p, 1e-  Next simplest: helium -2p 2n 2e-  li = lithium: 3p 3n 3e-  e: 6p 6n 6e-  o: 8p 8n 8e-  variations on atomic structure:  isotopes  have more/less neutrons than the most common form  eg. H (hydrogen) with 1p 1n 1e-  eg. C (carbon) 6p 7n 6e-  ions  having more/less e- than the most common form  eg. ionized hydrogen: 1p only or 1p 2e-  (diagram)  transfer  give electricity  electric current  have electron bump into atom, go into higher orbit  electron go into higher orbit, changes into energy of atom  internal energy  look @ hydrogen atom in more detail  1e- orbits 1p  the e- can “be” in any orbit (energy level)  but if it can’t exist in between energy levels, each type of atoms has a specific set of energy levels  it is possible for the e- to jump between different energy levels  eg. if the e- absorbs a photon of just the right energy, it can jump up one level  the energy of the photo is converted to internal energy in atom  photon = a piece or a particle of light  e- can also gain energy if the atom collides with others atoms or particle o process is called absorption  eg. on e- in a high level jumps to a lower level & emits a photon with specific energy or wavelength
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