Electromagnetic wave: Difference between revisions
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In [[physics]], an '''electromagnetic wave''' is a change, periodic in space and time, of an [[electric field]] '''E'''('''r''',''t'') and a [[magnetic field]] '''B'''('''r''',''t''). Examples of electromagnetic waves (in increasing [[wavelength]]) are: [[gamma radiation|gamma rays]], [[X-ray]]s, | In [[physics]], an '''electromagnetic wave''' is a change, periodic in space and time, of an [[electric field]] '''E'''('''r''',''t'') and a [[magnetic field]] '''B'''('''r''',''t''). Examples of electromagnetic waves (in increasing [[wavelength]]) are: [[gamma radiation|gamma rays]], [[X-ray]]s, | ||
[[ultraviolet light]], [[visible light]], [[infrared]], [[microwave]]s, and [[radio waves]]. All these waves propagate with the same speed ''c'', the [[speed of light]]. | [[ultraviolet light]], [[visible light]], [[infrared]], [[microwave]]s, and [[radio waves]]. All these waves propagate with the same speed ''c'', the [[speed of light]]. | ||
[[Image:Electromagnetic wave.png|center|thumb|550px|Electromagnetic wave. Electric component (red) in plane of drawing; magnetic component (blue) in orthogonal plane; propagation to the right. The wavelength is λ. ]] | [[Image:Electromagnetic wave.png|center|thumb|550px|Electromagnetic wave. Electric component (red) in plane of drawing; magnetic component (blue) in orthogonal plane; propagation to the right. The wavelength is λ. ]] | ||
In the figure we see a snapshot (i.e., a picture at a certain point in time) of the magnetic and electric fields in adjacent points of space. In each point, | In the figure we see a snapshot (i.e., a picture at a certain point in time) of the magnetic and electric fields in adjacent points of space. In each point, the [[vector]] '''E''' is perpendicular to the [[vector]] '''B'''. The wave propagates to the right, along an axis which we conveniently refer to as ''y''-axis. | ||
Assume that the snapshot is taken at time ''t'', then at a point ''y'' we see an arrow of certain length representing '''E'''(''y'',''t''). At a point in time Δ''t'' later, the same value of '''E''' (same arrow) is seen at ''y'' + ''c'' Δ''t''. The arrow seems to have propagated to the right with a speed ''c''. | Assume that the snapshot is taken at time ''t'', then at a point ''y'' we see an arrow of certain length representing '''E'''(''y'',''t''). At a point in time Δ''t'' later, the same value of '''E''' (same arrow) is seen at ''y'' + ''c'' Δ''t''. The arrow seems to have propagated to the right with a speed ''c''. | ||
[[Image:Overview electromagetic spectrum.png|right|thumb|275px|Schematic overview of electromagnetic spectrum. Vertical axis: wavelengths in meter. Examples: infrared extends from 8 ·10<sup>−7</sup> to 10<sup>−3</sup> m; radio from 10<sup>−4</sup> to about 10<sup>4</sup> m.]] | |||
If we focus on a fixed point ''y'', then in progressing time we see the two vectors '''E'''(''y'',''t'') and '''B'''(''y'',''t'') grow to a maximum value, then shrink to zero, become negative, going to a minimum value, and grow again, passing through zero, and growing to maximum value. In other words, when we plot '''E''' and '''B''' in the fixed point ''y'' as a function of time ''t'', we see the same sine-type function as in the figure. | |||
==External link== | |||
[http://www.spacewx.com/pdf/SET_21348_2004.pdf ISO 21348 Definitions of Solar Irradiance Spectral Categories] | |||
'''To be continued''' | '''To be continued''' | ||
Revision as of 08:38, 11 August 2008
In physics, an electromagnetic wave is a change, periodic in space and time, of an electric field E(r,t) and a magnetic field B(r,t). Examples of electromagnetic waves (in increasing wavelength) are: gamma rays, X-rays, ultraviolet light, visible light, infrared, microwaves, and radio waves. All these waves propagate with the same speed c, the speed of light.
In the figure we see a snapshot (i.e., a picture at a certain point in time) of the magnetic and electric fields in adjacent points of space. In each point, the vector E is perpendicular to the vector B. The wave propagates to the right, along an axis which we conveniently refer to as y-axis. Assume that the snapshot is taken at time t, then at a point y we see an arrow of certain length representing E(y,t). At a point in time Δt later, the same value of E (same arrow) is seen at y + c Δt. The arrow seems to have propagated to the right with a speed c.
If we focus on a fixed point y, then in progressing time we see the two vectors E(y,t) and B(y,t) grow to a maximum value, then shrink to zero, become negative, going to a minimum value, and grow again, passing through zero, and growing to maximum value. In other words, when we plot E and B in the fixed point y as a function of time t, we see the same sine-type function as in the figure.
External link
ISO 21348 Definitions of Solar Irradiance Spectral Categories
To be continued