A thin convex lens of focal length 10 cm is placed in contact with the concave lens of same material and of same focal length. The focal length of combination will be:

Question

A thin convex lens of focal length 10 cm is placed in contact with the concave lens of same material and of same focal length. The focal length of combination will be: (A) Zero (B) Infinity (C) 10 cm (D) 20 cm

Tardigrade Admin · Accepted Answer

According to the relation (1/ f )=(1/ f 1)+(1/ f 2) f =( f 1 f 2/ f 1+ f 2) =(10 ×(-10)/10+-10) =(-100/0)=∞

Q. A thin convex lens of focal length $10 c m$ is placed in contact with the concave lens of same material and of same focal length. The focal length of combination will be:

Zero

Infinity

$10 c m$

$20 c m$

According to the relation
$\frac{1}{f} = \frac{1}{f _{1}} + \frac{1}{f _{2}}$
$f = \frac{f _{1} f _{2}}{f _{1} + f _{2}}$
$= \frac{10 \times ( - 10 )}{10 +- 10}$
$= \frac{- 100}{0} = \infty$

Q. A thin convex lens of focal length 10cm is placed in contact with the concave lens of same material and of same focal length. The focal length of combination will be:

Zero

Infinity

10cm

20cm

According to the relation f1​=f1​1​+f2​1​ f=f1​+f2​f1​f2​​ =10+−1010×(−10)​ =0−100​=∞

Q. A thin convex lens of focal length $10 c m$ is placed in contact with the concave lens of same material and of same focal length. The focal length of combination will be:

$10 c m$

$20 c m$

According to the relation
$\frac{1}{f} = \frac{1}{f _{1}} + \frac{1}{f _{2}}$
$f = \frac{f _{1} f _{2}}{f _{1} + f _{2}}$
$= \frac{10 \times ( - 10 )}{10 +- 10}$
$= \frac{- 100}{0} = \infty$