Which statement correctly describes the principal foci of a thin lens?  
AA lens has only one focus, located on the image side
BThe two foci of a double convex or double concave lens are equidistant from the optical centre
CThe first focal point always lies farther from the lens than the second focal point
DA concave lens has no real geometric focus on either side
Answer & Solution
Correct answer: B. The two foci of a double convex or double concave lens are equidistant from the optical centre
A thin lens has two principal foci, one on each side, and for a symmetric thin-lens treatment they are equidistant from the optical centre. The focus on the side of the original light source is the first focal point; the other is the second focal point. So B is the correct statement.
Related questions
In a compound microscope, the lens placed near the object has which property compared withFor correcting myopia, a concave lens is used. According to the convention for lens power,The 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 is