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

Answer 1

Answer: (B)

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