PHYSICS FOR PRE UNIVERSITY

Friday, October 23, 2009

Wednesday, September 30, 2009

Interference is the addition (superposition) of two or more waves that results in a new wave pattern. Interference usually refers to the interaction of waves that are correlated or coherent with each other, either because they come from the same source or because they have the same or nearly the same frequency.

The principle of superposition of waves states that the resultant displacement at a point is equal to the vector sum of the displacements of different waves at that point. If a crest of a wave meets a crest of another wave at the same point then the crests interfere constructively and the resultant wave amplitude is greater. If a crest of a wave meets a trough of another wave then they interfere destructively, and the overall amplitude is decreased.

Optical path length

optical path length (OPL) is the product of the geometric length of the path light follows through the system, and the index of refraction of the medium through which it propagates
$\mathrm{OPL} = nd .\,$
A difference in optical path length between two paths is often called the optical path difference (OPD)

The refractive index, n, of a medium is defined as the ratio of the velocity, c, of a wave phenomenon such as light or sound in a reference medium to the phase velocity, v_p in the medium itself:
$n = \frac{c}{v_{\mathrm {p}}}.$

Tuesday, September 8, 2009

Lenses are classified by the curvature of the two optical surfaces. A lens is biconvex (or double convex, or just convex) if both surfaces are convex. If both surfaces have the same radius of curvature, the lens is equiconvex. A lens with two concave surfaces is biconcave (or just concave). If one of the surfaces is flat, the lens is plano-convex or plano-concave depending on the curvature of the other surface. A lens with one convex and one concave side is convex-concave or meniscus. It is this type of lens that is most commonly used in corrective lenses.