Question

$n$ the displacement method, the distance between the object and screen is$70cm$ and focal length of the lens is$16cm$. The separation of the magnified and diminished image positions of the lens is

• A. 17 cm
• B. 20.5 cm
• C. 25 cm
• D. 22.5 cm

Answer 1

Answer: (B)

$D=$ Distance of image from object; distance between two lens positions $=d$ and $f=$ focal length of convex lens.
$d=\sqrt{D^2-4fD}$
$=\sqrt{70^2-4\times 16\times 70}$
$=\sqrt{420}=20.5cm$