A doctor prescribes a lens with a power of P=−2.5 D to a patient. This lens is _____.
A concave lens, used to correct Myopia.
The power of a lens is defined as \(P = \frac{1}{f}\), where f is the focal length in metres. A negative power means a negative focal length, which is the characteristic of a concave (diverging) lens.
Myopia (short-sightedness) occurs when the eye's focal length is too short, causing distant images to focus in front of the retina. A concave lens diverges incoming light rays, effectively pushing the focal point back onto the retina — correcting myopia.
Hypermetropia (long-sightedness) is corrected by a convex (converging) lens with positive power, not a concave lens.
Hence, a lens with P = −2.5 D is a concave lens, used to correct Myopia.
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Important Questions from Optics
Who was the first one to use a glass prism to obtain the spectrum of sunlight?
Twinkling of stars is due to:
In which a convex mirror is used?
A. Rear View mirrors in vehicles
B. Glass windows
C. Makeup Mirror
D. Kaleidoscope
An object is placed 10 cm in front of a lens. The image formed is real, inverted and of same size as the object. What is the focal length and nature of the lens?
The power of a lens is -2.5 D. The type of lens and its focal length are respectively:
