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Old Jun 15th 2009, 02:03 PM   #1
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Converging lenses...causes dispersion?

Can converging lenses cause dispersion or can it only bring light rays together? Basically, I'm asking if it makes a difference if the curved part is facing the light source or not.

Based on my logic, if the curvy part is facing the light source; the light rays will converge (=be brought together at a fixed point) and if the curvy part is facing the opposite direction of the light source then the light rays will travel away from each other (=disperse).

Is my logic correct?

Any input would be greatly appreciated!
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Old Jun 16th 2009, 02:18 AM   #2
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Dispersion is where different wavelengths of light take different paths through an optical system usually resulting in polychromatic light being split into its colours. There are two physical
mechanism for this, being:

1. Material Dispersion: where the refractive index of a material depends on the wavelength,

E.g. Red light bends more than blue light outcoming from a prism. When white light passes, you can see a colour spectrum instead of white light.

2. Diffractive Dispersion: where light is diffracted from grating structure, here the angle
of diffraction depends directly on the wavelength of the light.

For a single lens, there are two phenomena called the spherical aberration and chromatic aberration. For spherical aberration, the light rays coming out do not pass through the same point. The effect of spherical aberration depends on the focal length and the diameter.

For chromatic aberration, similar to that mention above. Different colours would have different refractive index in lens causing different degree of bending and hence colour fringes observed.
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