concave lens

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Lens that possesses at least one surface that curves inwards. It is a diverging lens, spreading out those light rays that have been refracted through it. A concave lens is thinner at its centre than at its edges, and is used to correct short-sightedness (myopia).

After light rays have passed through the lens, they appear to come from a point called the principal focus. The distance between the principle focus and the lens is the focal length. A more curved lens will have a smaller focal length and will be a more powerful lens. The image formed by a concave lens is virtual, upright, and smaller than the object, and it cannot be projected onto a screen. The lens formula is used to work out the position and nature of an image formed by a lens: 1/u + 1/v = 1/f, where u and v are the distances of the object and image from the lens, respectively, and f is the focal length of the lens.

The flag's unusual 3:4 proportions are laid down by law. Green represents the forests. Blue symbolizes the Atlantic Ocean. Effective date: 9 August 1960. >>