Electromagnetic Spectrum - Scaling Visible And Invisible Light
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Electromagnetic Spectrum - Scaling Visible And Invisible Light

The wave nature of light presents the electromagnetic spectrum.

(a) What is a wave?
(b) Why are light waves electromagnetic?
(c) How is the electromagnetic spectrum scaled?

The strings:

S7P4A44 (Motion - Wave Motion).

The math:
Pj Problem of Interest is of type motion (wave-motion). The wave nature of light implies wave motion of light.

(a) A wave is a traveling disturbance that carry energy from one place to another. In other words, for a wave to occur, there must be a disturbance and the disturbance must be propagated. Disturbance is a disequilibrium from a resting or equilibrium state. Disturbance can be large scale or small scale visually. For example, a person who has been tilted by a friend out of his hammock where he was resting peacefully, has been disturbed. A pebble dropped in a quiet standing lake has disturbed the water molecules of the lake. Disturbance is propagated by the energy resulting from the vibrations it initiates. In the example of the pebble dropped in the lake, water molecules are disturbed at the point where the pebble is dropped, those molecules disturb nearby molecules and so on. This movement of energy outward from a vibrating source is a wave.

(b) Some waves require a medium (the matter in which the wave is moving) in which to propagate (e.g water wave). Such waves are called mechanical waves.

Some waves do not require a medium to propagate. Instead they disturb electric and magnetic fields. Such waves are called electromagnetic waves. In order words, electromagnetic waves can travel within or without a medium. The source of all electromagnetic waves is charge that is changing speed or direction. All electromagnetic waves have the same speed. Light waves are electromagnetic waves.

(c) All waves have three fundamental characteristics:
- Amplitude (greatest distance from rest to crest of a wave).
- Wavelength (distance between two consecutive similar point on a wave).
- Frequency (number of waves that pass a given point in a given amount of time usually in a second).

The various types of light waves differ in wavelengths and as a result in frequency also. The arrangement of light waves according to increasing frequency (decreasing wavelength) constitute the scaling of light. This arrangement is called the electromagnetic spectrum (figure 21.7).
Visible light is that part of the electromagnetic spectrum that the human eye can perceive naturally (i.e. unaided by technology other than normal vision lenses). In order words, the range of frequencies of visible light are within the range of frequencies the unaided human eye can perceive.
Invisible Light is that part of the electromagnetic spectrum that the human eye cannot perceive naturally (i.e. natural eyes need technological help). In order words, the range of frequencies of invisible light are not within the range of frequencies the unaided human eye can perceive.

Blessed are they that have not seen, and yet have believed. John 20:29