If f v and fR are the focal lengths of a convex lens for violet and red light respectively and Fv and FR are the focal lengths of a concave lens for violet and red light respectively, then we must have

Question

If f v and fR are the focal lengths of a convex lens for violet and red light respectively and Fv and FR are the focal lengths of a concave lens for violet and red light respectively, then we must have (A) fV > f R and Fv > F R (B) fV < f R and Fv > F R (C) fV > f R and Fv < F R (D) fV < f R and Fv < F R

Tardigrade Admin · Accepted Answer

F or a convex lens, fR > F V or fV < fR For a concave lens, focal length is negative. ∴ |FV| < |FR | or Fv > F R as the smaller negative value is bigger

Q. If $f_{v}$ and $f_{R}$ are the focal lengths of a convex lens for violet and red light respectively and $F_{v}$ and $F_{R}$ are the focal lengths of a concave lens for violet and red light respectively, then we must have

$f_{V} > f_{R}$ and $F_{v} > F_{R}$

$f_{V} < f_{R}$ and $F_{v} > F_{R}$

$f_{V} > f_{R}$ and $F_{v} < F_{R}$

$f_{V} < f_{R}$ and $F_{v} < F_{R}$

F or a convex lens, $f_{R} > F_{V} or f_{V} < f_{R}$ For a
concave lens, focal length is negative.
$∴ ∣ F_{V} ∣ < ∣ F_{R} ∣ or F_{v} > F_{R}$ as the smaller negative
value is bigger

Q. If fv​ and fR​ are the focal lengths of a convex lens for violet and red light respectively and Fv​ and FR​ are the focal lengths of a concave lens for violet and red light respectively, then we must have

fV​>fR​ and Fv​>FR​

fV​<fR​ and Fv​>FR​

fV​>fR​ and Fv​<FR​

fV​<fR​ and Fv​<FR​