Light

Physical Science

Atoms Absorb Energy• Matter exposed to energy (heat) causes the atoms to absorb

this energy• Atoms respond in 2 ways:

1. Atom moves faster 2. Electrons absorb energy and move to a

higher energy level (excited state)- These electrons are only briefly excited and give up

their extra energy (pulse of electromagnetic energy) as they return to a lower energy level (stable state)

- The frequency of this pulse of energy (electromagnetic waves) determines the form of energy: radio, heat, light, and x-rays (light family)

- For more information and a simulation, scroll down to electron shells at the link below,

- http://www.visionlearning.com/library/module_viewer.php?mid=51

Atoms Absorb Energy

- Electromagnetic waves

- Both electrical and magnetic fields

- Frequency

- The number of cycles of a wave occurring in 1 second

Dispersion and Colors• White light

• Mixture of colors in sunlight (RoyGBiv)• Separated with a prism

• Dispersion• Index of refraction

• The ratio of the speed of light in a vacuum to the seed of light in a material

• Index of refraction varies with wavelength• Wavelength

• The horizontal distance between successive wave crests or other successive parts of the wave

• Different wavelengths refract at different angles because they do not travel at the same speed (depends on frequency) so they slow down at different rates, bending at different angles

• Violet refracted most (shortest wavelength)• Red refracted least (longest wavelength)

Light has Wave Properties

1. Expand in circles

2. Rebound when strike a surface

3. Pass through each other

• Light waves do not need a medium so can travel through vacuum (space)

Light Interacts with Matter

• Interaction begins at surface and depends on• Smoothness of surface• Nature of the material• Angle of incidence

• Possible interactions• Reflection

• How we see objects that do not create their own light• Light bounces off a surface• Mirrors reflect light

• Refraction • Absorption• Transmission

Light Interacts with Matter

• Light that interacts with matter is reflected, transmitted, or absorbed, and all combinations of these are possible

• Materials are usually characterized by which of these interactions they mostly do, but this does not mean that other interactions are not occurring too• Transparent materials transmit light• Opaque materials do not allow transmission of light • Translucent materials allow some transmission of

light• Colors result from selective wavelength

reflection/absorption• Red objects reflect red wavelengths of light and

absorb all others

Refraction

• Light crossing a boundary surface and changing direction

• Reason: change in light propagation speed

• Moving to a medium with a slower propagation speed

• Light bends toward surface normal

• Moving to a medium with a faster propagation speed

• Light bends away from the normal

Magnitude of refraction depends on: •Angle that light strikes surface•Ratio of speed of light in the two transparent materials

Incident ray perpendicular to surface not refracted

Optics • The use of lenses to form

images (refraction)• Concave lenses

• Diverging lenses• Vision correction/in

association with other lenses

• Convex lenses• Converging lenses• Most commonly used lens• Magnifiers, cameras,

eyeglasses, telescopes, etc.

Study Websites

• Atoms Absorb Energy• http://www.upscale.utoronto.ca/PVB/Harrison/

BohrModel/Flash/BohrModel.html

• Shine and Shadow• http://www.learner.org/resources/series118.html

• Laws of Light • http://www.learner.org/resources/series118.html

• Pigments, Paint, and Printing• http://www.learner.org/resources/series118.html

GACE II Information- MG

Light Ray Model• Particle-like view• Photons travel in

straight lines• Applications

• Mirrors• Prisms

• Lenses

Wave Model• Traces motions of wave

fronts• Best explains

• Interference• Diffraction• Polarization

Properties of Light - Two Models

For more information scroll down to particles and waves at the link below,http://fuse.pha.jhu.edu/~wpb/spectroscopy/basics.html