Question

A concave lens and convex lens have same focal length of 16 cm each. They both are kept in contact. This combination is used to view an object 3.5 cm long, the image of this object is

Answer 1

The focal..length of convex lens is positive and concave lens negative, hence, combination
$\frac{1}{f}=\frac{1}{f_1}+\frac{1}{f_2}$
Given, $f_1=f_2$
$\frac{1}{f}=\frac{1}{f_1}-\frac{1}{f_2}=0$
$f=\infty$
The combination has infinite focal length. Hence, image of object is of same size.