A combination of convex and concave lenses has power 4 D. If the convex lens has power 5 D, the focal length of the concave lens will be

Question

A combination of convex and concave lenses has power 4 D. If the convex lens has power 5 D, the focal length of the concave lens will be (A) 100 cm (B) 100 cm (C)  -1 cm  (D)  (100/-9) cm

Tardigrade Admin · Accepted Answer

Power of combination P=P1+P2 ⇒ 4=5+P2 ⇒ P2=4-5=-1 D ∴ -1=P2=(100/f( cm )) ⇒ f=-100 cm

Q. A combination of convex and concave lenses has power $4 D$ . If the convex lens has power $5 D$ , the focal length of the concave lens will be

$100 c m$

$100 c m$

$- 1 c m$

$\frac{100}{- 9} c m$

Power of combination
$P = P_{1} + P_{2}$
$\Rightarrow 4 = 5 + P_{2}$
$\Rightarrow P_{2} = 4 - 5 = - 1 D$
$∴ - 1 = P_{2} = \frac{100}{f ( c m )}$
$\Rightarrow f = - 100 c m$

Q. A combination of convex and concave lenses has power 4D. If the convex lens has power 5D, the focal length of the concave lens will be

100cm

100cm

−1cm

−9100​cm

Power of combination P=P1​+P2​ ⇒4=5+P2​ ⇒P2​=4−5=−1D ∴−1=P2​=f(cm)100​ ⇒f=−100cm

Q. A combination of convex and concave lenses has power $4 D$ . If the convex lens has power $5 D$ , the focal length of the concave lens will be

$100 c m$

$100 c m$

$- 1 c m$

$\frac{100}{- 9} c m$

Power of combination
$P = P_{1} + P_{2}$
$\Rightarrow 4 = 5 + P_{2}$
$\Rightarrow P_{2} = 4 - 5 = - 1 D$
$∴ - 1 = P_{2} = \frac{100}{f ( c m )}$
$\Rightarrow f = - 100 c m$