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Final

NATS 1870 Study Guide - Final Guide: Experimentum Crucis, Electromagnetic Spectrum, Photon


Department
Natural Science
Course Code
NATS 1870
Professor
Robin Kingsburgh
Study Guide
Final

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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
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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
oprocess is called absorption
eg. on e- in a high level jumps to a lower level & emits a photon with
specific energy or wavelength
process is called emission
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