The power of a lens is calculated as the inverse of its focal length in meters. For a concave lens with a focal length of 2 meters, the power P is given by P = 1/f, where f is the focal length. Therefore, P = 1/2 = 0.5 dioptres. Since it’s a concave lens, its power is negative, so the power is -0.5 dioptres.

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## Introduction to Lens Power

*Understanding Optical Power*: The power of a lens is a crucial concept in optics, representing the lens’s ability to converge or diverge light. It is measured in dioptres and is inversely proportional to the focal length of the lens.

### Focal Length of Lenses

*Defining Focal Distance*: The focal length of a lens is the distance from the lens to its focus. For a concave lens, which diverges light, the focal length is considered negative, reflecting its diverging effect on light rays.

#### Concave Lenses

*Diverging Light Rays*: A concave lens is a type of lens that diverges light rays. This means that instead of converging light to a point, a concave lens spreads out light rays, making them appear to originate from a point behind the lens.

##### Calculating the Power of a Concave Lens

*Application of the Formula*: The power of a lens is calculated using the formula P = 1/f, where P is the power in dioptres and f is the focal length in meters. For a concave lens with a focal length of 2 meters, the calculation is straightforward.

###### Result of the Calculation

*Determining Lens Power*: Substituting the focal length into the formula, P = 1/2, we find that the power of the lens is 0.5 dioptres. However, since it is a concave lens, its power is negative, making the power -0.5 dioptres.

*Understanding the Optical Power of Concave Lenses*: Therefore, a concave lens with a focal length of 2 meters has an optical power of -0.5 dioptres. This negative value is indicative of the lens’s diverging properties and is essential in applications where spreading out light rays is required, such as in certain types of eyeglasses.

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