Which one of the following lenses would you prefer to use while reading very small letters printed on a label ?
[amp_mcq option1=”Convex lens of large focal length” option2=”Concave lens of large focal length” option3=”Convex lens of small focal length” option4=”Concave lens of small focal length” correct=”option3″]
This question was previously asked in
UPSC CAPF – 2009
A Convex lens of small focal length is preferred for reading very small letters printed on a label.
To read small letters, a magnifying glass is used. A magnifying glass is a convex lens. A convex lens forms a magnified, virtual, and erect image when the object is placed within its focal length. The magnification power of a simple magnifying glass is given by M = 1 + (D/f), where D is the least distance of distinct vision (approx. 25 cm) and f is the focal length of the lens. To achieve higher magnification, the focal length (f) must be smaller.