Question

A lens has a focal length of 0.1 m .Find the image distance when the object distance is

Answer 1

Answer:

A) 0.125 m  (the image is real)

B) -0.4 m (the image is virtual)

Explanation:

For both situations we will use the Lens Equation:

$\frac{1}{f}=\frac{1}{v}+\frac{1}{u}$ (1)

Where:

$f=0.1 m$ is the focal length

$u$ is the distance between the object and the lens

$v$ is the distance between the image and the lens

Isolating $v$:

$v=\frac{uf}{u-f}}$ (2)

Knowing this, let's begin with the answers:

A) When $u=0.5 m$

$v=\frac{(0.5 m)(0.1 m)}{0.5 m-0.1 m}}$

$v=0.125 m$ The image is real

B) When $u=0.08 m$

$v=\frac{(0.08 m)(0.1 m)}{0.08 m-0.1 m}}$

$v=-0.4 m$ The negative sign indicates the image is virtual