One dioptre is the unit of measurement for the optical power of a lens, defined as the power of a lens with a focal length of one meter. In other words, if a lens has a focal length of one meter, its optical power is said to be 1 dioptre. This unit is used to quantify the convergence or divergence of light caused by a lens, with positive dioptres indicating converging lenses and negative dioptres indicating diverging lenses.

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## Introduction to Lens Power

*Understanding Optical Power*: The power of a lens is a measure of its ability to converge or diverge light rays. It is a key parameter in optics, determining how much the lens can bend light rays and thus affect the image formation.

### Definition of Dioptre

*Unit of Lens Power*: One dioptre (D) is the unit of measurement for the optical power of a lens. It is defined as the power of a lens that has a focal length of one meter.

#### Focal Length and Lens Power

*Inverse Relationship*: The power of a lens is inversely proportional to its focal length. This means that a lens with a shorter focal length has a higher power and vice versa. A lens with a focal length of one meter, therefore, has a power of 1 dioptre.

##### Positive and Negative Dioptres

*Converging and Diverging Lenses*: Positive dioptres indicate converging lenses, like those used in reading glasses, which bring light rays together. Negative dioptres, on the other hand, are associated with diverging lenses, like those used in myopia correction, which spread light rays apart.

###### Practical Implications

*Importance in Optics and Vision Correction*: The concept of dioptres is crucial in optics and vision correction. It helps in quantifying the degree of correction needed in eyeglasses and contact lenses, allowing for precise adjustments to achieve the desired focus and clarity in vision.

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