Question

Column I		Column II
A	Lens of power + 2.0 D	1	Concave lens of focal length 40 cm
B	Lenses of combination of power +0.25 D and +0.25 D	2	Scattering of sunlight
C	Lens of power -2.0 D	3	Convex lens of focal length 50 cm
D	Lenses combination of power -6 D and +3.5 D	4	Concave lens of focal length 50 cm

• A. $ (A) \rightarrow (1) ; (B) \rightarrow(2) ; (C) \rightarrow(3) ; (D) \rightarrow (4)$
• B. $(A) \rightarrow (3); (B) \rightarrow (1); (C) \rightarrow (4); (D) \rightarrow (2)$
• C. $(A) \rightarrow (4); (B) \rightarrow (3); (C) \rightarrow (1); (D) \rightarrow (2)$
• D. $( A ) \rightarrow(3) ; (B) \rightarrow (4); (C) \rightarrow (2) ; (D) \rightarrow (1)$

Answer 1

Answer: (B)

(i) $P=+2.0 \Rightarrow f=\frac{1}{+2.0} \times 100\, cm =+50\, cm$
(Positive power convex lens)
(ii) $P=P_1+P_2=(+0.25)+(+0.25)=+0.50 D$
$f=\frac{1}{P}=\frac{1}{+0.5} \times 100 \,cm =200 \,cm$
(iii) $P=-2.0 \Rightarrow f=\frac{1}{-2.0} \times 100\, cm =-50\, cm$
( -ve power concave lens)
(iv) $P=P_1+P_2=(-6.0)+(+3.5)=-2.5 \,D$
$f=\frac{1}{P}=\frac{1}{-2.5} \times 100 \,cm =-40\, cm$