Two thin lenses of focal lengths f1 and f2 are in contact and coaxial. The power of the combination is

Question

Two thin lenses of focal lengths f1 and f2 are in contact and coaxial. The power of the combination is (A) √(f1/f2) (B) √(f2/f1) (C) (f1-f2/f1 f2) (D) (f1+f2/f1 f2)

Tardigrade Admin · Accepted Answer

If two thin lenses of focal lengths f1 and f2 are placed in contact coaxially, then equivalent focal length of combination is (1/F)=(1/f1)+(1/f2)-(0/f1 f2)=(1/f1)+(1/f2) Power for the combination is P=(1/F)=(1/f1)+(1/f2)=(f1+f2/f1 f2)

Q. Two thin lenses of focal lengths $f_{1}$ and $f_{2}$ are in contact and coaxial. The power of the combination is

$\frac{f _{1}}{f _{2}}$

$\frac{f _{2}}{f _{1}}$

$\frac{f _{1} - f _{2}}{f _{1} f _{2}}$

$\frac{f _{1} + f _{2}}{f _{1} f _{2}}$

Q. Two thin lenses of focal lengths f1​ and f2​ are in contact and coaxial. The power of the combination is

f2​f1​​​

f1​f2​​​

f1​f2​f1​−f2​​

f1​f2​f1​+f2​​

If two thin lenses of focal lengths f1​ and f2​ are placed in contact coaxially, then equivalent focal length of combination is F1​=f1​1​+f2​1​−f1​f2​0​=f1​1​+f2​1​ Power for the combination is P=F1​=f1​1​+f2​1​=f1​f2​f1​+f2​​

Q. Two thin lenses of focal lengths $f_{1}$ and $f_{2}$ are in contact and coaxial. The power of the combination is

$\frac{f _{1}}{f _{2}}$

$\frac{f _{2}}{f _{1}}$

$\frac{f _{1} - f _{2}}{f _{1} f _{2}}$

$\frac{f _{1} + f _{2}}{f _{1} f _{2}}$