Collect the information about the lenses available in an optical shop. Find out how the focal length of a lens may be determined by the given 'power of lens. (AS4)

An optical shop consists of different lenses according to the eye problem a patient has. Like a myopic patient uses a concave lens while a patient suffering from hypermetropia uses convex lens. Old aged people used bifocal lens and so on. People prescribed a sphere and a cylinder prescription have astigmatism of the eye and can be given atoric to correct it.So the following lists include all the types of lenses available in an optical shop:

• Plano convex lens

• Double convex lens

• Plano concave lens

• Double concave lens

• Cylindrical lens

• Achromatic lens

• Aspheric lens

• IR lens

• UV lens

• Atoric lens

The SI unit of power is diopter (D). 1 D lens focuses rays of light at a distance of 1 metre. Thus the focal length of such lens is 1 metre (100 cm). So if power is given then focal length will be: