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Rapid Review
Electromagnetic Radiation
Electromagnetic waves consist of fields of electric and magnetic energy that are oscillating perpendicularly to the direction of propagation of the wave. The electric and magnetic fields are in phase with each other and are also perpendicular to each other. Since the fluctuations are perpendicular to the direction of propagation, electromagnetic waves are transverse waves.
Electromagnetic Spectrum
|
Type of Radiation (in order of decreasing frequency) |
Comments |
Approximate frequency |
|
g rays |
Produced by radioactive decay; nuclear reactions |
� 1020 Hz |
|
X-rays |
Produced by deceleration of high-speed electrons, e.g. X-ray tube. |
� |
|
Ultraviolet |
Produced by electrons going from higher energy orbitals to lower higher energy orbitals |
� |
|
Visible light |
Produced by electrons going from higher energy orbitals to lower higher energy orbitals, e.g. electric light bulb |
1014 Hz |
|
Infrared
(heat waves) |
Produced by and causes movement of atoms and molecules, vibration of bonds. Used in IR spectroscopy. |
� |
|
Microwaves (higher-frequency radio waves) |
� | |
|
Lower-frequency radio waves |
Used in NMR spectroscopy |
106 Hz |
Polarization
Since electromagnetic waves are transverse, they can be polarized. This means that the electric field fluctuates along a single plane as opposed to fluctuating in every plane (for simplicity, the magnetic field component is ignored).
A polarizing material placed in the path of a beam of unpolarized light will absorb the electric field components in a certain plane. The transmitted light will thus be polarized in the plane perpendicular to plane in which absorption is occurring. The intensity of the light transmitted is half the intensity of the light incident on the polarizing material.
Disorders of Vision
|
Scientific name of disorder |
Common name of disorder |
Basic problem |
Treatment |
|
Myopia |
Nearsightedness |
Cannot focus on distant objects |
Diverging lenses |
|
Hyperopia |
Farsightedness |
Cannot focus on near objects |
Converging lenses |
Lens Aberrations
|
Aberration |
Explanation |
Measures to reduce it |
|
Spherical aberration |
The rays from a single point on the object are not focused to a single point on the image. |
Use an aperture so that only rays close to the principal axis can pass through the lens. Or use 2 lenses instead of 1. |
|
Chromatic aberration |
Dispersion in the lens causes different colors to to be focused at different points along the principal axis. |
Use an achromatic lens (a converging and diverging lens in tandem). This combination rejoins separated colors. |
