The power of a lens (P) is related to its focal length (f) by the formula P = 1/f, where f is in meters. For a lens with a power of +1.5 D, the focal length is f = 1/1.5 meters, which equals approximately 0.67 meters or 67 cm. The positive sign of the power indicates that the lens is a converging lens, typically used to correct farsightedness.

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## Introduction to Lens Power and Focal Length

*Understanding Lens Power*: The power of a lens, measured in dioptres (D), is a key optical property that indicates its ability to converge or diverge light. It is directly related to the focal length of the lens, providing insight into its function.

### Prescription Details

*Lens Power Prescribed by Doctor*: A doctor has prescribed a corrective lens with a power of +1.5 dioptres. The positive value of the power suggests a specific type of lens, which can be identified by calculating its focal length.

#### Calculating Focal Length

*Using the Power Formula*: The relationship between the power (P) of a lens and its focal length (f) is given by P = 1/f, where f is expressed in meters. To find the focal length of a lens with a power of +1.5 D, we rearrange this formula to f = 1/P.

##### Determining the Focal Length

*Focal Length Calculation*: Substituting the power value into the formula, f = 1/1.5, we find that the focal length is approximately 0.67 meters or 67 cm. This value is crucial in identifying the type of lens.

###### Identifying the Type of Lens

*Nature of the Lens*: The positive focal length indicates that the lens is a converging lens. Converging lenses, such as convex lenses, are characterized by their ability to bring light rays together.

*Characteristics of the Prescribed Lens*: Therefore, a lens with a power of +1.5 dioptres has a focal length of approximately 67 cm and is a converging lens. This type of lens is commonly used in corrective eyewear to address issues like farsightedness, where converging lenses help focus light onto the retina.

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