Question

A double convex lens made of glass of refractive index $1.56$ has both radii of curvature of magnitude $20cm$. If an object is placed at a distance of $10cm$ from this lens, the position of the image formed is

• A. $22.86$ same side of the object
• B. $22.86$ opposite side of the object
• C. $44.89$ same side of the object
• D. $44.89$ opposite side of the object

Answer 1

Answer: (A)

Here, $R_1=20cm,R_2=-20cm,u=-10cm$
and $\mu =1.56$
Using lens make'rs formula,
$\frac{1}{f}=\left(1.56-1\right)\left(\frac{1}{20}+\frac{1}{20}\right)$
$\Rightarrow f=\frac{20}{0.56\times 2}=17.86cm$
Now, from lens equation,
$v=\frac{uf}{u+f}=\frac{-10\times 17.86}{-10+17.86}=-22.86cm$
Since $v$ is negative, the image will be formed on the same side as that of object.