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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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School
Department
Natural Science
Course
NATS 1870
Professor
Robin Kingsburgh
Semester
Fall

Description
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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