Magnification In Lenses - Practice Questions & MCQ

Magnification in Lenses-

Magnification produced by a lens is defined as the ratio of the size of the image to that of the object. 

For the derivation let an object is placed whose height is h and the image height is h'. Let us consider an object is placed on the principal axis with its height h perpendicular to the principal axis as shown in the figure. The first ray passing through the optic centre will go undeviated. The second ray parallel to the principal axis must pass through the focus F' The image is formed where both the light rays intersect. By this, we get an image of height h'. So mathematically, magnification can be written as - 

                                                                                  $\mathbf{m}=\frac{\mathbf{h}^{\prime}}{\mathbf{h}}$

Like the mirror equation, we can derive the formula of magnification in terms of the position of the object and image. For this, consider the figure given below - 

As the triangle, ABO and $\mathrm{A}^{\prime} \mathrm{B}^{\prime} \mathrm{O}$ is similar so we can write that -

$
\frac{A^{\prime} B^{\prime}}{A B}=\frac{O B^{\prime}}{O B}
$

So,

$
\begin{aligned}
& \frac{h^{\prime}}{h}=\frac{v}{u} \\
& m=\frac{h^{\prime}}{h}=\frac{v}{u}
\end{aligned}
$