Home › Tamil Nadu SSLC (Class 10) › Physics › Optics › For correcting myopia, a concave lens is used. A…
For correcting myopia, a concave lens is used. According to the convention for lens power, the power of such a corrective lens is which sign?
APositive
BAlways equal to one
CNegative
DZero
Answer & Solution
Correct answer: C. Negative
1. By convention, a concave (diverging) lens has negative focal length.
2. Power is $P = \dfrac{1}{f}$, so a negative $f$ gives a negative power.
3. Myopia is corrected with a concave lens, so its power is negative.
4. A positive power would correspond to a convex lens, which corrects hypermetropia instead.
_Source: Samacheer Kalvi (TN SCERT) Class 10 Science, Unit 2 Optics "Power of a Lens", p.30_
Related questions
In a compound microscope, the lens placed near the object has which property compared withThe ability of the eye lens to focus on both nearby and distant objects by changing its foFor a hypermetropic person, the near point has shifted to 1.5 m. Using $f = \dfrac{dD}{d-DA myopic person can clearly see objects only up to 4 m and wants to see objects up to 20 mThe eye defect presbyopia, in which a person loses the power of accommodation for both neaIn a myopic (short-sighted) eye, where is the image of a distant object formed relative toTwo thin lenses of powers $+5\ \text{D}$ and $-2\ \text{D}$ are placed in contact. What isThe power of a lens is $-4\ \text{D}$. What is its focal length?